The Angels overcame an early six-run deficit by scoring eight times in the third. They then fell behind 11-9, came back to take a 12-11 lead in the top of the ninth and wound up going into extra innings when Cody Ross tied it for Boston with a homer in the bottom half of the inning.
Kendrys Morales put Los Angeles back in front with a solo shot in the 10th and Wells produced his RBI double later in the inning to give the Angels a two-run advantage. They needed it when Dustin Pedroia brought Boston within one with a run-scoring single in the bottom of the 10th.
The teams combined for 38 hits.
Pedroia had five RBI, three of them on a second-inning homer. Wells contributed three RBI for the Angels, one coming on a bases-loaded walk in the eighth-run third inning and another with a solo homer in the top of the ninth.
Ernesto Frieri (3-0) worked the ninth and 10th innings for the Angels and gave up two runs, but still picked up the victory.
The loss went to Alfredo Aceves (2-8), who retired only three men while giving up five runs. He was the seventh of eight Boston pitchers.