The seven-time Cy Young winner felt like he was missing his usual sharpness, but still earned his 345th win, allowing one run in six innings in Houston's 5-2 victory.
"I didn't feel like I had a lot of life," Clemens said, "and then Brad came out and said it's as good as ever."
Clemens (4-4) struck out five and allowed four hits, yielding two runs or fewer for the eighth time in 10 starts. His 2.32 ERA since June 22 leads NL starters.
"He said he felt like he was underwater was the term I think he used," Ausmus said. "That translates to being a little sluggish. I thought he had good life on his fastball."
Ausmus also helped out Clemens with a pair of RBI singles and Morgan Ensberg hit a three-run homer for the Astros, who have won seven of nine. Houston earned its first series sweep since taking three in a row from the Chicago Cubs at Wrigley Field in mid-June.
The Astros now stand just 2½ games behind Cincinnati in the crowded NL wild-card race.
"We have to do it every night," Clemens said. "We know where we stand. This bunch is up to that challenge."
Manager Jim Tracy was disappointed his team blew chances to win Thursday's series finale.
"It came down to an opportunity that got away from us and an opportunity they capitalized on," he said.
Ensberg's 20th homer of the season was his first since he came off the disabled list on Aug. 1 after recovering from a bruised right shoulder.
"I don't know if it's so much a relief," Ensberg said, "but it definitely felt good."
Before Ensberg's home run, the Astros couldn't do much against starter Tom Gorzelanny (2-3). The 24-year-old left-hander was almost as good as Clemens, allowing five hits with six strikeouts. He also walked five and the two run-scoring singles by Ausmus.
Gorzelanny walked Ensberg and Luke Scott in the second, and Ausmus singled sharply single to center for his first RBI since he hit his third career grand slam in Arizona on Aug. 5.
In the fourth, Scott beat out a grounder that second baseman Jose Castillo fielded before throwing over the head of first baseman Xavier Nady. With one out, Ausmus singled to center again, securing his sixth multi-RBI game of the season.
Like Clemens, Gorzelanny felt like he struggled with his control.
"It was one of those days I had to battle through," he said. "I was not really hitting my spots. I was just grinding."
Clemens retired nine consecutive batters before Nate McLouth's one-out single in the sixth. Jack Wilson followed with a line-drive double to left, but McLouth only reached third.
Sanchez, the NL's batting leader, then sent a fly to right to score McLouth.
Clemens was finished after Jeromy Burnitz walked and Nady singled starting the seventh. He was replaced by Chad Qualls, who gave up a tying three-run homer after relieving Clemens in a 7-6 loss to Arizona on July 30. Qualls did the job this time.
After Castillo bunted into a fielder's choice, Paulino beat out a slow bouncer to load the bases. Joe Randa pinch-hit for Gorzelanny and grounded to Ensberg, who stepped on third and threw to Berkman, the Astros' 122nd double play of the season.
Qualls said Clemens complimented him after escaping the jam.
"It was good to get a second chance and get out of a tight situation," said Qualls.
Salomon Torres replaced Gorzelanny, and Craig Biggio doubled down the left-field line to start the final rally. Torres intentionally walked Berkman, and John Grabow struck out Aubrey Huff.
Tracy then yanked Grabow for rookie Matt Capps, who'd given up three home runs in his last eight outings. Ensberg whiffed on Capps' first pitch, then hit the second one into the left-field seats.
"Capps comes in and throws him a good slider on the first pitch," Tracy said. "But on the second one, it wasn't obviously as good as the first. He got it up a little bit. That can happen to anybody."
- Willy Taveras singled to extend his hitting streak to 13, a career high.
- Clemens made his 681st career start, tying Pud Galvin for ninth.
- The Astros failed to score in the first inning for the first time in six home games against Pittsburgh this season.