With the game tied 2-2 in the ninth, Valencia greeted Koji Uehara (4-1) with a lead-off triple.
Alexi Casilla came in to run and slid home with the decisive run when Wieters followed by lining a fly ball to right field.
Tommy Hunter (6-4) earned the decision and Jim Johnson finished up with his 46th save as the Orioles won a second straight and pulled within two games of American League wild-card co-leaders Texas and Tampa Bay.
Chris Davis pounded a franchise-record 51st homer of the season for Baltimore with a score-tying solo blast in the sixth.
Dustin Pedroia went deep for the AL East-leading Bosox, whose magic number to win the division crown fell to three with Tampa Bay's loss to Texas Tuesday.
Kate Middleton recycles dress at movie premiere
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'