Feldman weaved his way through a few jams over the first four innings, limiting damage along the way, but Seattle broke through with a four-run fifth inning.
Feldman gave up seven hits and five runs over 4 2/3 innings to fall to 2-3 with an ERA of 5.70 in six O's starts. He is 1-3 with an ERA of 7.66 in four home starts.
The O's starters have hit a rough patch, with just three quality starts over the last nine games and an ERA of 6.06 in that span.
Michael Saunders hit a three-run homer off T.J. McFarland in the fifth, scoring two of Feldman's inherited runners. He added a two-run shot off Darren O'Day in the ninth for a two-homer, five RBI night and his fifth career multi-homer game.
O's pitching has allowed seven homers in this series and 12 over the last four games.
Matt Wieters hit a solo homer in the second, and Manny Machado hit one in the fourth for the Orioles. They went to the seventh down 6-2 but rallied for two more runs not long after manager Buck Showalter was ejected by home plate umpire Larry Vanover for arguing a strike call with Nick Markakis at the plate. Chris Davis had a sac fly - and Wieters an RBI single - during the rally.
Machado added a double in the eighth. It snapped a 22-game stretch without one and was the 40th of the year for the major league leader in doubles.
This game featured a very strange O's double play in the top of the eighth. Raul Ibanez singled off the right-field wall with two on and one out, but the O's got a runner at the plate and then Ibanez trying to get back to first for a 9-4-3-2 double play.
The Orioles fall to 61-50 as they lost to Seattle for just the third time in the last 13 games, and the Mariners ended a seven-game losing streak at Camden Yards dating to May 10, 2011.