Pegg's longest 'Run'

First-time director David Schwimmer digs himself a deep hole in the opening minutes of “Run Fat Boy Run.” His lead, played by Simon Pegg, leaves a very pregnant Thandie Newton at the altar on their wedding day. Raise your hands if you’re itching to root for their reunion.

“Run,” opening March 28, follows how Pegg’s character, Dennis, desperately tries to erase the biggest mistake of his life. The journey is quite bumpy, both for the character and the audience. We get Farrelly brothers’ slapstick one moment, credible character arcs the next. But Schwimmer has an ace in the hole with Pegg, the slacker hero from “Shaun of the Dead” who could make the most distasteful cad charismatic.

Dennis’s odds of wooing Newton’s Libby back look pretty bleak, and that’s before we’re introduced to her new beau, Whit (Hank Azaria, the buffest character actor in history). She’s smitten, and she doesn’t give Dennis much thought except when it’s time to drop off their son with him on weekends.

But when Dennis hears about an upcoming marathon, he decides it’s the perfect way to show Libby he’s changed. Easier said than done, since Dennis has only three weeks to prepare for the race, and he can barely run a block without collapsing into a wheezing wreck. “Fatboy” veers between sweet rom-com formula and indie-land, and the results can be jarring. Do we really need a scene in which Dennis and his cousin pal (Dylan Moran) pop a monstrous blister?

Pegg and Newton don’t exactly spark as a romantic couple, but they’re each individually good enough to overcome the lack of chemistry. The film’s final scenes could use some serious editing, but audiences will be rooting hard for Dennis to make it to the finish line nonetheless.

(Photo: Hank Azaria and Simon Pegg leg it out, center, in "Run Fat Boy Run")