As you may have heard, the defending National League champion Houston Astros have a new no. 5 starter. Good as it is to see Roger Clemens, probably the best pitcher in baseball history, back on a mound, the freak show aspect of his latest return from retirement has somewhat overshadowed the bigger story: For the third year in a row, the Astros are digging themselves out of a massive hole and preparing to make a run at October.

June 4 was the first day the St. Louis Cardinals played without Albert Pujols, who hasn’t played a game since and still leads the National League in home runs and runs batted in. It was right around then that the Astros got hot; after play was concluded on the June 4, they were 27-30, 8.5 back in the NL Central and 5.5 games out of the wild card lead.

When Clemens took the hill last night, his team was 37-35,six games behind St. Louis and two behind Cincinnati, a team that gave the Mets a tough series this week but is likely fade as the season progresses. In an incredibly weak league, you might even consider the Astros the wild card favorites right now coming off the recent hot streak.

This sort of thing is by now standard for the Astros. Two years ago they were 44-44 before the All-Star break and ended up clinching their playoff spot on the last day of the season; last year they started off 15-30 and again clinched in their final game. Two years ago, the stories were Carlos Beltran and manager Phil Garner, under whom the team went 44-26 in the second half after Jimy Williams was fired. Last year, the story was Clemens, Roy Oswalt, and Andy Pettitte, a historically great trio of starters who carried the team to the pennant with virtually no help from the rest of the team.

The storyline this year will be all about Clemens. If the Astros win out, his return to the team will be viewed as the turning point that lifted them to a third straight October; should they fall just short, either he or the team will be criticized for his sitting out the first two and a half months of the season, which can be painted either as the inevitable outcome of the team’s refusal to offer him salary arbitration last winter without an assurance he would in fact be returning to the team, or as a wise move meant to prevent Clemens from breaking down in the fall as he did the last two years, thus ensuring he was at his strongest when the team needed him most.

It’s easy to understand why this will be so, but in fact the fate of the Astros isn’t really tied to their ornery ace. That’s because it’s enormously difficult for one player to make that much difference over three and a half months.

Clemens will be replacing Fernando Nieve in the Houston rotation. Nieve is no great prize: In 65 innings, he’s struck out 42, walked 20, and given up 14 home runs for a 4.71 ERA. Still, in 11 starts he’s given the Astros a good chance of winning more often that not. In only two games – one in which he threw 3 2/3 innings and gave up six runs, and another in which he gave up five runs in 5 2/3 – has he completely spit the bit.

After a couple of early starts in which he was pulled early despite pitching well, Nieve has almost always pitched at least into the sixth inning and rarely given up more than two runs. These things are subjective, but of those 11 starts I’d say nine were strong performances in which the Astros could expect a win so long as the offense played as usual (they’re averaging 4.65 runs per game) and the bullpen was solid. That’s probably about what you could expect him to do if he or a similar pitcher made another 20 starts: throw a few gems, get blown out a few times, and keep the team in the game the majority of the time.

Clemens can’t do much more than that. Let’s be optimistic. Say he makes 20 starts, in which he throws six or seven innings and gives up two or three runs, never getting blown out. Impressive as that would be, in total there would be something like four games in which he’d give the team a notably better chance than a Nieve-type would. To be sure, apart from the example he sets for teammates, his ability to draw fans, and so on, there are enormous on-field benefits Clemens brings over Nieve and his ilk: He can dominate the strongest offensive clubs in the league, he’s going to be much more consistent, and so forth, and you can’t minimize the importance of that. But if everything goes right, the Astros are going to win four games that they wouldn’t have won otherwise because of Clemens, and while four games is huge, there’s a reason that’s the absolute best case: It’s not particularly likely.

If the Astros win, it will be in part because of Clemens, but more because Oswalt stays healthy, Pettitte returns to form, Lance Berkman and Morgan Ensberg keep slugging, and Garner plays all his cards right. Clemens is a great player, and it’s wonderful that he’s back. (Sort of.) But it’s still a team game, and he’s not going to make or break the team’s season.

tmarchman@nysun.com