He has not pitched well on the road this year or well against righties while the Cards hit very well at home and very well against lefties (more info below on this).
With the Giants down 3-1 in the series, he pitched 7.2 innings with 6 hits, 6 K's, 1 BB (intentional) and zero runs. That gives him a "game score" (a Bill James stat) of 72. Here is how it is calculated
1.Start with 50 points.
2.Add 1 point for each out recorded, so 3 points for every complete inning pitched.
3.Add 2 points for each inning completed after the 4th.
4.Add 1 point for each strikeout.
5.Subtract 2 points for each hit allowed.
6.Subtract 4 points for each earned run allowed.
7.Subtract 2 points for each unearned run allowed.
8.Subtract 1 point for each walk.
In 32 starts during the regular season, he had an average game score of 49.53 (I came up with an average game score of 46.4 in the NL this year, so Zito was not much better than that).
He is not a big game pitcher, either. His start against the Reds in the division series had a game score of 42. His previous 8 playoff starts averaged 55.13. Only 3 were 68 or higher with a high of 79 (way back in 2001).
It is not like he came on at the end of the season, either. His average game score was 51.38 in his last 13 starts with a high of 66 and only 4 60+ games.
He did have 4 starts this year with a game score of 72 or higher. But those were generally against below average hitting teams.
83 vs. Colorado (in Denver). Rockies OPS+ this year as 91
78 vs. Cubs at home. Cubs OPS+ was 85
74 vs. Braves in Atl. Braves OPS+ was 90
72 vs. Dodgers at home. Dodgers OPS+ was 90
(according to Baseball Reference, the NL league average OPS+ was 94, not 100 for some reason).
The Cardinals were tied for 1st in OPS+ this year with 107 (tied with Giants). Zito had an ERA+ this year of 84. He was hurt last year and only pitched 53 innings. In 2010, his ERA+ was 94.
The Cards had an OPS at home of .786 and .731 on the road while the league average was .718. They had .787 vs lefties but .835 vs. lefty starters. Zito allowed an OPS at home of .726 and .796 on the road. It was .823 vs. righties and .559 vs. lefties (the Cards started 5 righties, a switch hitter and 2 lefties).
Now in his career it is .705 vs. righties and .701 vs. lefties, so maybe righties don't especially bother him. But this year he gave up 1 HR per 9 IP, which was the league average. His SO/BB ratio was 1.63, far below the league average of 2.50. I doubt anyone could have expected his performance last night. He is hardly an ace or stopper.
The average game score by a lefty during the regular season against the Cards was 45.8. The highest by a lefty in Busch was 60 (Bumgarner). So Zito was well above both of those.
Only 3 Lefty pitchers during the regular season had a game score of 72 or higher against the Cards (out of 45 starts)
Johan Santana 90
Gio Gonzalez 82
Clayton Kershaw 79
In the Division series, Gio Gonzalez had 55 and 46. I don't think the Nats had any other lefty starters. Bumgarner had 22 in game 1. I think that is all the lefty starts agains the Cards in the playoffs besides Zito. Did I miss any?