Happ, the second of three rookie pitchers to start a game in a crucial four-game series against the Mets, will begin his road back to the Major Leagues immediately, as he was sent to Triple-A Ottawa after the game.
The 24-year-old lefty surrendered five earned runs on three homers over four-plus innings. He was the first pitcher to give up two home runs in the first inning of a big-league debut since Kansas City's Wes Obermueller did it in 2002.
The 6-foot-6 southpaw was the sixth Phillies pitcher this season to make his debut and the 24th pitcher Philadelphia has used this season, three fewer than the club record of 27, which was set in 2002. By the time the series ends on Sunday, the Phillies will have used three pitchers with a combined seven Major League starts.
J.D. Durbin was roughed up over four innings during the first game of Friday's doubleheader, and ace Cole Hamels had a subpar outing in the nightcap. Durbin and Happ combined to allow three homers to the red-hot Carlos Beltran.
"You just go out there and ask them to do what they do," Ryan Howard said of the team's young pitching. "Just go out there and do what got you here."
Happ said on Thursday that he thought he could throw several quality innings and have his offense back him up.
The Phillies' third and final run of the afternoon came on Howard's 19th home run, which flew over the "Have a ball" sign and into the right-field second deck, tying the game at 3 in the fourth inning.
But just when it seemed like Happ was settled in, Beltran hit a two-run shot in the fifth inning. He added a seventh-inning blast and shoved the Phillies to the brink of a sweep.
Happ, who brought with him from Triple-A concerns about his high pitch counts, racked up 94 on Saturday. He pitched three scoreless innings after Paul Lo Duca and David Wright homered in the opening frame.
"I felt good; I even felt good in the first inning," Happ said. "That pitch to Wright, I left the pitch down. I kind of got in the groove and started feeling good with breaking pitches in the next few innings."
The task to avoid the sweep on Sunday falls to Kyle Kendrick, who, with three career starts, is the veteran of the Phillies' recent callups.
Kendrick has tossed six innings in each of his three starts to this point.
"We kind of got into a fix where we don't have any other choices with injuries and stuff," Manuel said. "Then all of a sudden, we had the doubleheader, and we run into a series where we had to throw what we got. That's how it goes. We got some real good players who fight hard, but the big thing is, can we fight all year?"
Manuel said on Saturday that the return of Brett Myers and Tom Gordon to the bullpen would strengthen the bullpen. So, too, would a healthy Freddy Garcia and Jon Lieber, but those two veterans aren't expected back this season.
The Phillies are familiar with their situation by now, and emphasized after Saturday's game that there was plenty of time to remedy injury problems and division deficits.
"It's tough," Shane Victorino said. "But we did it to them. We swept them [at Shea Stadium]; they took three from us right now. There's so much season left, and that's what I keep looking at."
With this weekend filed away in the "that's baseball" file, Manuel said his players are still focused on winning.
Aaron Rowand showed his commitment with an effort familiar to Mets fans. The Phillies center fielder made a play at Beltran's second home run, landing at the top of the fence on his waist in an effort to rob the Mets outfielder of his second blast.
However, the ball deflected off the side of his glove and bounced among the members of the Phillies' impressed bullpen.
"When he first hit it, I thought it was long gone," Victorino said. "Then it kept dropping."
"I hit my waist [on the fence], and it jolted my glove," said Rowand, who made a running catch against the Mets last year, when he crashed into the wall and broke his nose and orbital bone.
The home run counted, Beltran scored again in the ninth and finished with four hits, tying a career high.
The Mets have hit .280 against Phillies' pitching over the first three games with nine home runs.
"We got in a spot where we had to throw young pitchers at them," Manuel said. "We got a young guy going tomorrow, and we have to come out winning tomorrow's game."