The Toronto Blue Jays will be looking to improve the starting rotation ahead of next season and pitchers like Happ have a chance to show they belong as the disastrous 2013 campaign draws to a close.
It did not go well for left-hander on Thursday night.
Happ allowed four runs in 4 1-3 innings as the Los Angeles Angels beat the Blue Jays 4-3 to complete a three-game sweep.
"I'm just trying to prove to myself more than anything else," he said. "I hope to go out and finish strong."
But twice he could not hold the lead on Thursday as the Blue Jays (67-79) lost despite four hits, including a home run, from Jose Reyes to go along with three hits from Moises Sierra.
Kole Calhoun had two hits with a home run for the Angels (70-76) and right-hander Garrett Richards (7-6) pitched 6 2-3 innings to win his third straight decision.
"He kept us in the game," Blue Jays manager John Gibbons said of Happ. "The thing that bit us the last two nights is two times (Wednesday) night and two times tonight we take the lead and don't get the shut down inning and give it right back. That's what kills you. That's a huge part of baseball.
"We're not throwing out our top-notch lineup right now, we're scratching for runs, so our starters have got to step up. We've got to find a way to get a shut down inning and we haven't done that the last two games."
Happ (4-6) lamented the missed opportunity to do just that.
"You want to give your team a chance to win," he said. "We got the lead and gave it right back. You'd like to have some shutdown innings when we do get the lead like that."
Richards allowed three runs on nine hits and a walk while striking out four as he improved to 4-1 in his last five outings.
"He got a little better as the game went on," Angels manager Mike Scioscia said. "I didn't think Garrett was as sharp tonight ... but he had some movement on his fastball, which got him through. Still, he pitched deep into the game and in the middle innings there was no doubt his stuff picked up."
Ernesto Frieri pitched the ninth for his 33rd save despite allowing a two-out double to Reyes and a walk to Munenori Kawasaki.
Happ needed 87 pitches in his short outing as he surrendered six hits and two walks while striking out six.
The Blue Jays opened the scoring in the first inning after Reyes and Kawasaki led off with singles. Reyes took third when Brett Lawrie grounded into a double play and scored on Adam Lind's double to right.
The Angels tied it in the second when Happ walked Chris Iannetta with two outs before surrendering singles to Calhoun and Grant Green.
"I think the assumption is that I made bad pitches," Happ said. "But as I go look back at it, I try to be honest as I can with myself, and the breaking ball to Green in the second inning I would like to have that pitch back. But (I was) really trying to be aggressive out there and they found a way. I'm going to keep working and try to figure this thing out but it's tough."
The Angels took a 2-1 lead in the third on a throwing error by Toronto centre-fielder Anthony Gose. Erick Aybar singled with one out, and after Mike Trout walked, Trumbo flied out to Gose, who made an ill-advised throw to third to try to catch Aybar. The throw short-hopped Lawrie and Aybar scored as Trout took second on the play.
The Blue Jays took a 3-2 lead in their third when Reyes hit his 10th homer of the season on the first pitch to tie the game. Kawasaki and Sierra then doubled to put Toronto into the lead.
But Calhoun tied it with one out in the fourth on his seventh homer of the season.
After one-out doubles by Aybar and Trout gave the Angels a 4-3 lead in the fifth, Neil Wagner replaced Happ.
Michael Kohn replaced Richards after Reyes doubled with two out in the seventh. Kohn walked Kawasaki before striking out Lawrie.
Notes: Attendance at Rogers Centre was 20,767. ... Blue Jays 1B Edwin Encarnacion (left wrist sprain) missed his fourth consecutive game and is still listed as day to day. ... Blue Jays CF Colby Rasmus (left oblique strain) says he could return to the lineup this weekend. ... Blue Jays RHP Todd Redmond (3-2, 4.40 earned-run average) will start against Orioles RHP Bud Norris (10-11, 4.12 ERA) in Friday's opener of a three-game series against Baltimore at Rogers Centre. ... Trout scored his 100th and 101st runs in Wednesday's 5-4 win over the Blue Jays to become the third Angels player to record back-to-back seasons with at least 100 runs scored, joining Don Baylor and Troy Glaus.