The Red Sox are off to a strong start at 5-2 under new manager John Farrell. They finished last in the AL East last season with a 69-93 record under Bobby Valentine, who was fired after one season.
Buchholz gave up three hits and three walks and struck out eight. Last Wednesday he allowed one run in seven innings in a 7-4 win over the New York Yankees.
Andrew Bailey blanked the Orioles in the eighth before Joel Hanrahan allowed a solo homer by Adam Jones, his first, in the ninth, but got his third save.
Buchholz allowed the first batter to reach base in four innings but only one runner advanced to second.
The Orioles put the leadoff runners at first in the first two innings, Nate McLouth with a single and Chris Davis with a walk, but neither moved up. With two outs in the third, singles by Manny Machado and Nick Markakis put runners at first and second before Jones took a third strike.
Davis led off the fourth with a walk but was forced out at second on a grounder by Matt Wieters. J.J. Hardy then grounded into a double play, ending the inning.
In the fifth, McLouth drew a two-out walk, but Machado flied out to right fielder Shane Victorino. Buchholz finally pitched a perfect inning in the sixth when Markakis grounded to first, Jones flied to right and Davis struck out looking. Buchholz walked Wieters leading off the seventh then retired the next three batters, striking out two and completing an impressive 113-pitch performance.
The Red Sox managed just four runners in the first six innings on two singles and two walks but none got past first base.
Nava walked with two outs in the second before Johnny Gomes popped out to second baseman Ryan Flaherty. Victorino started the fourth with a single but was caught stealing. Pedroia then walked before Napoli grounded into a double play.
Nava then singled with one out in the fifth, but Chen struck out Gomes and got David Ross to ground out to Flaherty.