Romero was brought in trying to preserve Philadelphia's two-run lead with the bases loaded and two outs. But Davis singled up the middle on a 3-1 fastball, garnering the two runs that ended up as the difference in the Phillies' 4-3 loss.
Romero gave up a single to the next batter he faced before being pulled.
"Lately, it seems like I've lost a little bit of my command," Romero said. "I felt that my first couple pitches I was a little timid, but then I started being aggressive. It just happened that a ground ball up the middle, a jam shot -- there's nothing I can do about that."
Davis has hit well (.314 average) against left-handers this season. But Romero has now gone three consecutive appearances without retiring a batter -- a career-long -- and he has issued 26 walks in 32 innings this season. Though his ERA remains at 3.66, those aren't the results the Phillies are expecting from their premier left-handed option out of the bullpen.
"I don't know if he's not trusting his stuff or not," said Phillies manager Charlie Manuel. "It looks to me like everything's down or way in on lefties. I don't know. We need J.C. to pitch good for us."
Philadelphia has two other left-handed relievers, Antonio Bastardo and Mike Zagurski. Both are young and largely untested, and Bastardo has allowed six runs in his past 10 appearances.