Roy Halladay and Tim Lincecum have combined to win four Cy Young awards, but only one has pitched like an ace so far this season.
Halladay looks to continue his solid start while Lincecum hopes to bounce back from a pair of rough outings as the Philadelphia Phillies visit the San Francisco Giants in the opener of a three-game set Monday night.
The right-handers have faced each other twice, with Lincecum winning Game 1 and Halladay taking Game 5 of the 2010 NL championship series.
Halladay's win marked his only victory against the Giants, improving to 1-3 with a 5.97 ERA in five career starts.
Lincecum won both of his outings against the Phillies in 2011 and is 5-2 with a 2.71 ERA in 12 games versus Philadelphia including the postseason.
Halladay (2-0, 0.60 ERA), who won a Cy Young with Toronto in 2003 and another with the Phillies in 2010 after Lincecum won the previous two NL awards, is coming off consecutive stellar outings.
He beat Pittsburgh 1-0 on April 5 after allowing two hits over eight innings, then gave up one run in seven innings of a 7-1 win over Miami on Wednesday.
Lincecum (0-1, 12.91 ERA) hasn't been nearly as good. He allowed five runs and eight hits in 5 1-3 innings of a 5-4 loss to Arizona in the Giants' opener April 6, then was chased after giving up six runs in 2 1-3 innings of Wednesday's 17-8 loss to Colorado.
The Phillies (4-5) will hope for another off day from Lincecum to build off their offensive outburst in an 8-2 win over the New York Mets on Sunday, salvaging the finale of a three-game series.
Philadelphia scored two runs in the first two games combined and have scored three or fewer six times this season. Some offseason acquisitions keyed Sunday's victory as Juan Pierre, 6 for 12 with two triples and a double lifetime off Lincecum, went 3 for 4 while Ty Wigginton drove in four runs and Laynce Nix had an RBI double.
"They're new on our team and it definitely takes them a while to get the feeling they belong," manager Charlie Manuel said. "I know how much they want to impress you. It takes them a while to get used to our team and feeling good about themselves."
The offensive display was welcomed as Philadelphia has struggled to score while missing Ryan Howard and Chase Utley due to injuries.
"It shows our guys we can score runs and we can knock them in," Manuel said.
The Giants (4-5) scored less than four runs for the first time this season in a 4-1 loss to Pittsburgh on Sunday that snapped a three-game winning streak. They also found out closer Brian Wilson will have season-ending surgery to repair damage to his pitching elbow.
"My spirits aren't down," Wilson said. "I know a lot of people are sad. I know Giants fans are probably going to look at this as like a huge loss. But we have the best bullpen in the league.
"I don't think they're going to falter. I think we're going to take the West no matter what."
Manager Bruce Bochy said he'll initially try a closer-by-committee with Santiago Casilla, Sergio Romo and Javier Lopez.
The Phillies outscored the Giants 15-6 in taking three of four in San Francisco last season.