The Philadelphia Phillies assembled the best starting rotation in a generation this offseason when they signed Cliff Lee in December to complement Roy Halladay, Roy Oswalt and Cole Hamels.

Cole Hamels is off to a 9-2 start with a 2.49 ERA for the first-place Phillies. (Tom Mihalek/AP)

Each of the Phillies’ Four Aces has an ERA of 3.38 or better, and they sport a combined record of 29-15 even as the Phils’ offense has scored at a slightly-better-than-average clip of 4.1 runs a game..

What makes this expected early-season dominance unexpected is the unlikely ace who has proved to be the most effective.

Halladay – the reigning Cy Young Award winner – still has the staff’s best stuff, and Lee showed how good he can still be when he tossed a two-hit shutout on Thursday.

But the Phillies’ starter who has consistently been the best this season has been Hamels.

Except for his dominant run in the 2008 playoffs that led to a World Series MVP Award, Hamels has largely been underappreciated on a national level since he came up in 2006.

This season, he is reaching the peak of his potential and has turned into the home-grown staff ace the Phillies’ management knew he would be before it brought in the other three stud veterans.

Hamels allowed six runs on seven hits in 2 2/3 innings in his first start of the year on April 5 against the Mets. Since then, Hamels has been as good as anybody in the game.

Halladay is still the ace among aces on the Phillies’ staff, but consider his numbers this season next to Hamels’s.

Roy Halladay (15 starts): 9-3, 2.56 ERA, 1.04 WHIP, .243 opponent BA, 9.13 K/9

Cole Hamels (14 starts): 9-2, 2.49 ERA, 0.92 WHIP, .203 opponent BA, 8.94 K/9

It’s interesting that a doubleheader this week forced a shake-up in the Phillies’ rotation, and Hamels will now pitch the day before Halladay at least in the immediate future.

Barring something catastrophic, the Phillies should cruise to their fifth consecutive division title, and Halladay still likely will be their eventual Game 1 starter in a playoff series.

But the Phillies would look pretty good with Cole Hamels starting in Game 2.