Most of the day's most interesting matches are early in the schedule. That's certainly a good thing considering the late matches might not get started at all.
Matches to Watch
Men's 1st round (Djokovic Region): Tommy Haas  vs. Guillaume Rufin
Advanced Baseline clay ranking: Haas No. 14 | Rufin No. 74
At 35 years old, Haas has produced some exciting results over the last few months. He beat Tomas Berdych and Roger Federer last summer, worked his way back into the Top 20, and took out players like Novak Djokovic, Nicolas Almagro, John Isner, Gilles Simon, and Florian Meyer this spring. In terms of clay rankings, he is probably the second-best player remaining in the Djokovic Region and could make a stellar run in the French Open ... if he can handle the best-of-5 format, anyway. He has not advanced beyond the third round of a major since reaching the 2009 Wimbledon semifinals, and while he has seen plenty of strong results in best-of-three tournaments, his age begins to show as matches creep on. And matches tend to creep on at the French Open.
Women's 1st round (Sharapova Region): Sam Stosur  vs. Kimiko Date-Krumm
Advanced Baseline clay ranking: Stosur No. 5 | Date-Krumm No. 99
Sam Stosur is probably going to have far too much for Kimiko Date-Krumm to handle, but this is Tuesday's most interesting "styles make fights" matchup, with Stosur's power and spin matching up with Date-Krumm's flat baseline game. Beyond that, however, Date-Krumm makes Tommy Haas seem young. She reached the French semis in 1995 (the same year young American Madison Keys was born), retired for more than a decade, and began a comeback at age 37. Now 42, she's chugging right along. She reached the third round at the Australian Open, and while her stay at the French should be short, she's there. That's pretty awesome.
Men's 1st round (Djokovic Region): Novak Djokovic  vs. David Goffin (Match 2, Court Philippe Chatrier)
Advanced Baseline clay ranking: Djokovic No. 2 | Goffin No. 90
On Monday, we got a "form check" look at Rafael Nadal as he took on Daniel Brands. The verdict: He's fine, really, but he's going to have to take it out of third gear if he wants to cruise through the opening rounds. Now we get a look at Djokovic, the other French favorite. Djokovic's opponent, David Goffin, is not particularly strong on clay, but he pulled a couple of upsets and took a set from Roger Federer at least year's French Open, and like Nadal, Djokovic will have to at least kick into fourth gear to move on. He'll do so, but Goffin should test him at least a bit.
Men's 1st round (Nadal Region): Stan Wawrinka  vs. Thiemo De Bakker (Match 3, Court 1)
Advanced Baseline clay ranking: Wawrinka No. 7 | De Bakker No. 77
Stan Wawrinka is great on clay and has had himself a lovely spring -- he took countryman Roger Federer to three long sets at Indian Wells, he took out Andy Murray in Monte Carlo, he whipped David Ferrer to win in Portugal, and he beat Jo-Wilfried Tsonga and Tomas Berdych to reach the finals at Madrid. He suffered a thigh injury that kept him out of the Rome Masters, however, so it will be interesting to see if he can maintain his form through a series of five-set matches. His first test (after a couple of extra luck-of-the-draw rest days) comes late Tuesday. Maybe.
Women's 1st round (Azarenka Region): Klara Zakopalova  vs. Kaia Kanepi (Match 3, Court 4)
Advanced Baseline clay ranking: Zakopalova No. 43 | Kanepi No. 8
Kaia Kanepi has made plenty of noise through the years -- she has reached the quarterfinals of four slams, including two French Opens; clay is by far her best surface (as the Clay AB rankings attest), but despite that, and despite her run to the Brussels Open title last week (and subsequent jump into the WTA Top 30), she was unseeded for this tournament. That's silly, honestly, and now Klara Zakopalova could pay for the French Open's mistake. Zakopalova is ranked just two spots ahead of Kanepi in the WTA rankings and is far less accomplished on clay. Kanepi could make another run toward the quarterfinals if she can advance past Zakopalova on Tuesday.
Balance of Power
With each daily preview, we'll take a look at the top-ranked (according to AB clay rankings) remaining members of each region of the draw. The seeds don't really mesh too well with clay-court competence.
2. Novak Djokovic 
14. Tommy Haas 
17. Alexandr Dolgopolov 
25. Pablo Andujar
26. Philipp Kohlschreiber 
27. Janko Tipsarevic 
31. Fernando Verdasco
37. Grigor Dimitrov 
None of the best clay-court players from this 'region' have begun play yet, and if the rain continues, some will get all the way to Wednesday without having done so.
Nadal Region of Complete Destruction
1. Rafael Nadal  - advanced to second round
7. Stan Wawrinka 
10. Richard Gasquet  -- advanced to second round
15. Benoit Paire 
18. Kei Nishikori  -- advanced to second round
21. Fabio Fognini  -- advanced to second round
22. Albert Ramos -- defeated in first round by Jerzy Janowicz
28. Jerzy Janowicz  -- advanced to second round
46. Florian Mayer 
This region has held form for the most part, though Daniel Brands certainly threw a scare into Nadal for most of two sets.
3. David Ferrer  -- advanced to second round
6. Tomas Berdych  -- defeated in first round by Gael Monfils
8. Nicolas Almagro  -- advanced to second round
12. Gael Monfils -- advanced to second round
13. Tommy Robredo  -- advanced to second round
23. Ernests Gulbis -- advanced to second round
24. Kevin Anderson  -- advanced to second round
30. Albert Montanes -- advanced to second round
It really was poor luck for Berdych to draw Monfils this early; but Berdych also blew a triple break point in the fifth set. He certainly had his chances. Regardless, Monfils' reward for beating the second-best clay-court player in the region is a shot at the sixth-best clay-court player in the region. Monfils-Gulbis will be a fascinating second-round match. And the winner could face Tommy Robredo. Seriously, this region is absolutely loaded with clay prowess.
4. Roger Federer  -- advanced to second round
11. Juan Monaco  -- defeated in first round by Daniel Gimeno-Traver
16. Jo-Wilfried Tsonga  -- advanced to second round
20. Marin Cilic  -- advanced to second round
29. Jarkko Nieminen -- advanced to second round
33. Gilles Simon  -- advanced to second round
36. Jeremy Chardy  -- advanced to second round
43. Daniel Gimeno-Traver -- advanced to second round
44. Jan Hajek -- advanced to second round
Juan Monaco was up two sets on Daniel Gimeno-Traver, then fell apart, leaving this region even weaker than it was before.
1. Serena Williams  -- advanced to second round
10. Angelique Kerber  -- advanced to second round
15. Svetlana Kuznetsova -- advanced to second round
17. Ekaterina Makarova  -- defeated in first round by Svetlana Kuznetsova
21. Roberta Vinci  -- advanced to second round
23. Caroline Wozniacki  -- advanced to second round
27. Romina Oprandi -- defeated in first round by Elina Svitolina
28. Varvara Lepchenko  -- advanced to second round
47. Petra Vetkovska -- advanced to second round
52. Sorana Cirstea  -- advanced to second round
Good Kuznetsova showed up on Monday, as did good Wozniacki. Serena is still an obvious, overwhelming favorite here, but she could certainly get a nice quarterfinal test from either Kerber, Kuznetsova, or Wozniacki. Or, hell, Varvara Lepchenko, who looked quite good in disposing of Mirjana Lucic-Baroni.
4. Sara Errani  -- advanced to second round
7. Agnieszka Radwanska  -- advanced to second round
9. Ana Ivanovic  -- advanced to second round
11. Simona Halep -- defeated in first round by Carla Suarez Navarro 12. Venus Williams  -- defeated in first round by Urszula Radwanska
16. Carla Suarez Navarro  -- advanced to second round
22. Nadia Petrova  -- defeated in first round by Monica Puig
25. Sabine Lisicki  -- advanced to second round
29. Julia Goerges  -- defeated in first round by Zuzana Kucova
31. Maria-Teresa Torro-Flor -- advanced to second round
60. Madison Keys -- advanced to second round
67. Mallory Burdette -- advanced to second round
This region has been the least predictable so far, with four of the top eight players according to Clay AB losing in the first round. Errani and Radwanska both looked great, however.
3. Victoria Azarenka 
6. Na Li  -- advanced to second round
8. Kaia Kanepi
14. Maria Kirilenko 
24. Yaroslava Shvedova 
30. Flavia Pennetta -- defeated in first round by Kirsten Flipkens
32. Alize Cornet 
33. Anabel Medina Garrigues -- defeated in first round by Na Li
35. Bethanie Mattek-Sands -- advanced to second round
36. Paula Ormaechea
If Kanepi lives up to her rather aggressive AB ranking, we could see a lovely fourth-round match between Kanepi and Na Li ... if Na survives Bethanie Mattek-Sands and, potentially, Yaroslava Shvedova first.
2. Maria Sharapova  -- advanced to second round
5. Sam Stosur 
13. Petra Kvitova 
18. Jelena Jankovic 
19. Dominika Cibulkova 
20. Lucie Safarova 
34. Jamie Hampton
37. Shuai Peng
This region could also be severely impacted by rain Tuesday.