And he will start against the Rockies at Citizens Bank Park on Wednesday.
But will he start again?
"I think that's something that we'll go over when it's time," manager Charlie Manuel said.
Trading for Lee without surrendering a Major League piece bumped Rodrigo Lopez to the bullpen. Somebody will follow suit once Pedro Martinez returns and Philadelphia again has more pitchers than slots.
Lee, Cole Hamels and Joe Blanton are safe, and pitching coach Rich Dubee said it would be "pretty tough" to try a six-man rotation. That means that Martinez, Jamie Moyer or Happ will likely be the odd man out.
"Jamie's pitching [Tuesday night], Happ's pitching [Wednesday] night," Manuel said, declining to speculate on the team's plans. "What kind of a message does that send a guy?"
Happ has been fantastic this season. He had won every decision before losing his past two starts and is still 7-2 with a 2.97 ERA.
Yet he could also be an attractive reliever because he has experience in the bullpen. Chan Ho Park was the Phillies' fifth starter out of Spring Training, and Happ made 12 relief appearances before the pair swapped roles. In 21 2/3 innings, the 26-year-old lefty surrendered 14 hits and just six runs (2.49 ERA).
"He didn't hang his head one bit, and pitched very, very well," Dubee said. "[Happ] did great. Knock on wood, he's had a very solid year so far. ... Experience is a big thing. And again, success is a big thing. He's got both of them."
Happ tossed 2 1/3 scoreless innings of relief in his one career appearance against Colorado.
PHI: LHP J.A. Happ (7-2, 2.97 ERA)
Happ had been rumored to be part of a trade that would bring Roy Halladay from Toronto, but the trade never materialized. Happ has been effective pitching out of rotation and bullpen this season. It remains to be seen where he will end up once Cliff Lee and Pedro Martinez both join the 25-man roster, but for the moment he remains a starter.
COL: LHP Jorge De La Rosa (9-7, 4.68 ERA)
De La Rosa won a franchise-record seventh consecutive start on Thursday against the Mets, giving up two runs on three hits in 6 1/3 innings. De La Rosa chipped in with a double, scoring the go-ahead run for the Rockies in the seventh inning. He'll look to extend his streak to eight wins against a Phillies' franchise that has given him problems in the past. De La Rosa is 0-2 with an 8.79 ERA in five career games against the Phils, including three starts. He was lit up for seven runs (six earned) in 3 2/3 innings in his only career start at Citizens Bank Park. Shane Victorino is 3-for-6 off De La Rosa with a home run while Jimmy Rollins is 3-for-7.
The Phillies enter Wednesday with 30 wins from left-handed pitchers, tied with the White Sox for the Major League lead. ... Philadelphia went 5-0 against Colorado last season and took two of three at Coors Field earlier this year. ... Second baseman Chase Utley began this series with a 19-game hitting streak against Colorado, but went 0-for-3 on Tuesday.
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Official game notes
WPHT 1210, WUBA 1480 (Español)
Thursday: Phillies (Cliff Lee, 8-9, 3.02) vs. Rockies (Aaron Cook, 10-3, 3.88), 1:05 p.m. ET
Friday: Phillies (Joe Blanton, 7-5, 4.02) vs. Marlins (Ricky Nolasco, 7-7, 5.00), 7:35 p.m. ET
Saturday: Phillies (Cole Hamels, 7-6, 4.68) vs. Marlins (TBD), 7:05 p.m. ET