That brought up Jones, who scorched a pitch to right field that Wells dived to grab, but it caromed off his glove and Quintanilla raced home with the game-winner as the Orioles recorded their 12th straight extra-inning win.
Darren O'Day (6-0) was credited with the victory thanks to two scoreless frames for second-place Baltimore, which notched its fourth straight triumph overall and pulled to within 4 1/2 games of the American League East-leading New York Yankees.
J.J. Hardy's three-run homer highlighted a seventh-inning rally that saw the O's charge back from a 7-3 deficit.
Matt Wieters socked a pair of solo shots for the victors.
Kyle Seager belted a three-run homer and Miguel Olivo added a bases-empty blast for the Mariners.