Max Scherzer posted a 4.43 ERA in 2011.
These things are not necessarily in opposition to one another. Scherzer didn't give up a lot of hits this season, or a lot of walks. With 174 strikeouts in 195 innings this season, he's obviously capable of pitching effectively, and occasionally pitching brilliantly. To say nothing of his mid-90s fastball.
Scherzer didn't pitch a shutout this season, and isn't likely to pitch one today, not having already thrown 82 in five innings.
His second- and third-best starts all season came against the White Sox; in April he shut them out for eight innings on four hits, and in September he shut them out for seven innings on five hits.
Scherzer's best start in 2011?
On the 4th of May, Scherzer held the New York Yankees scoreless for eight innings on four hits and two walks, and he struck out nine Yankees.
That was in Comerica Park, though, where home runs go to die.
It's still fairly early. But if Scherzer can keep the Yankees off the board for two more innings, he'll have saved his very best start for his most important start.