The Houston lefty certainly accomplished his goal.
Happ threw a two-hitter and rookie Brett Wallace had a career-high three hits and drove in a run to help the Astros beat the struggling Cardinals 3-0.
It was a complete turnaround from his last meeting with the Cardinals, when he allowed a career-high seven earned runs in just one-plus innings.
"I wasn't dwelling on it, but certainly that was as bad of a start as I've had maybe in my life and it was tough to take at the time," he said. "I saw looking ahead after that game that I was going to get another chance and you always want to prove to that team that that wasn't you out there. They got me pretty good last time. But this was a different story."
It was another tough loss for the Cardinals, who have dropped six of seven and fallen six games behind Cincinnati in the NL Central race.
"It's not like there's just no hope," St. Louis shortstop Brendan Ryan said. "Even for me, I'm struggling as bad as I have ever struggled, but I still think every day I come to the field I am going to get a couple hits and help the team win. I don't know. It's just very frustrating."
Happ earned his fourth complete game and third shutout of his career. The Astros acquired the 27-year-old in the deal that sent Roy Oswalt to the Phillies last month. His last complete game was Aug. 27, 2009 against the Pirates, and his last shutout was Aug. 5 of the same year against the Rockies.
"It's been a while since I've felt that comfortable throwing first-pitch strikes and had that confidence and I was just kind of feeding off that," Happ said. "They were putting the ball in play and we were making plays."
Cardinals manager Tony La Russa raved about Happ.
"He had everything working tonight," La Russa said. "We saw him pitch against Philadelphia, and he's a talented guy. Everything he threw, nothing over the middle, changed speeds, different breaks. It was an outstanding exhibition of pitching."
Happ (5-2), who hadn't gone longer than 6 1/3 innings this season, struck out four and walked one.
"After his last outing against these guys I think he wanted to come back and really have a good game and he was almost even better than that. He was outstanding," Astros manager Brad Mills said. "I know he wanted to show himself and prove to himself more than anything else and I think he did without a doubt."
Wallace, who is batting just .215, hit an RBI-double in the seventh that bounced low off the wall in left center field to score Chris Johnson and push Houston's lead to 2-0. Johnson singled to start the inning.
"I was excited to get a big hit for us," Wallace said. "I knew I probably got it over his head. So it's just exciting to contribute offensively for once."
The Astros added a run later in the inning when Wallace came home on Jason Castro's double-play grounder.
Randy Winn singled with one out in the first inning, but Albert Pujols grounded into a double play to end the inning. Colby Rasmus walked with no outs in the third before Happ retired the next 16 batters. Happ didn't allow another hit until Yadier Molina singled to shallow left field with one out in the eighth.
Wallace showed his defensive skills in the eighth when he caught a fly ball from Rasmus and tagged first for an unassisted double play to end the inning.
Cardinals starter Jake Westbrook (1-3) allowed nine hits and three runs in seven innings in his sixth start since coming to St. Louis as part of a three team trade with Cleveland.
"I'm sure he's not very happy here," La Russa said. "Early on, we didn't support him very well defensively and then we don't score well. He's done a good job. We're really impressed with him."
Lee walked with one out in the fourth and reached third on a single by Wallace with two outs, but Tommy Manzella's fly ball to left field ended the inning.
The Cardinals activated RHP Jason Motte from the 15-day disabled list and optioned INF/OF Allen Craig to Triple-A Memphis. ... Houston INF Jeff Keppinger (toe) is on a rehabilitation assignment with Double-A Corpus Christi, but could return to the team as soon as Wednesday. ... Astros' reliever Matt Lindstrom, on the disabled list with a back strain, is scheduled to throw one inning and 20-25 pitches for Corpus Christi on Tuesday.