Lazio go into the break with their noses in front of ten man Roma in the 139th Derby della Capitale.
Thunder and lightning put paid to the floodlights, as the overcast Olimpico was plunged into darkness in the opening minutes.
From the resulting corner, Totti's pinpoint cross met the head of the unmarked Lamela to give the Giallorossi the lead, after nine minutes. It was Lamela's eighth strike of the season. The frontman has now hit the net in six consecutive games, surpassing Totti's feat of five.
Lazio were affording Totti too much space in the early stages, and he nearly punished them, forcing Marchetti to pull off two consecutive saves within a minute.
It took Lazio over 20 minutes to wake up and get to grips with the game. Cristian Ledesma saw Mauro Goicoechea off his line and tried a quick free-kick, but the ball got caught in the puddles and Alvaro Gonzalez was unable to pounce.
Roma's young custodian was called into action midway through the first half to palm Klose's header wide. Gonzalez saw a shot deflect wide, then as we passed the half hour mark, Hernanes sent a free-kick into the stands, and Abdoulay Konko headed just over as Lazio continued to press.
Candreva drew the sides level ten minutes before the break, drilling a free-kick from 35 yards into the net. Goicoechea misjudged the flight of the ball and ended up flapping it into the net with his hands.
The equaliser briefly woke Roma up. Five minutes before the break, Marchetti had to be at full stretch to tip Totti's cross-turned-shot over the bar.
Lazio quickly went on the counter-attack with Candreva. The winger laid the ball off to Klose, who took a touch and drilled wide from the edge of the box. The German went one better with his next chance.
Roma allowed Hernanes to run with the ball, and when his shot hit a puddle, Klose was on hand to pick the ball up in the box and smash it underneath Goicoechea. The veteran marksman has kept up his record of scoring in every Rome derby in which he has played, taking his tally to three in three games.
With yellow cards flying around, De Rossi made Roma's second half task that much harder when he had his Mike Tyson moment of madness. Amazingly, De Rossi's dismissal is the sixth in just four derby games.