Joba Chamberlain struck out three and allowed one hit in 1 1-3 innings before Mariano Rivera got three outs for his 13th save in 13 tries.
Before the game, New York put starter Ian Kennedy (right shoulder) on the disabled list. That increased speculation that Chamberlain would join the starting rotation as soon as next week, but manager Joe Girardi insisted the hard-throwing reliever still needed to increase his endurance and strength.
"I can't tell you 100 percent that he is going to take that spot," Girardi said before the game. "I have to see what happens tonight first."
Chamberlain threw 28 pitches, an abbreviated outing that probably did not test his perseverance. But he threw hard in the bullpen in the bottom of the ninth.
Johnny Damon had three hits for the Yankees after getting four in a 10-9 loss Tuesday night. Damon beat out a bases-loaded grounder to first base in the ninth when Jamie Walker was late covering the bag, an RBI single that gave New York a 4-2 lead.
Melvin Mora had three hits, including a two-run homer, and Brian Roberts also had three hits for Baltimore. But the rest of the lineup went 3-for-27.
Orioles starter Jeremy Guthrie (2-6) allowed three runs and six hits in seven innings, striking out four and walking none. Baltimore has scored only eight runs in the six games he's lost this year.
After the Orioles got a runner to third base with one out in the first inning and failed to score, New York went up 1-0 in the second when Hideki Matsui hit a bloop double and came home on a single by Giambi.
Mora put Baltimore ahead in the third with his seventh home run of the season and second in two nights.
Giambi tied it in the fourth with a drive that landed on Eutaw Street beyond the right-field wall. There have been 42 such homers in the 17-year history of Camden Yards; Giambi has hit three of the last five, including one Tuesday night.
New York went up 3-2 in the fifth. Melky Cabrera hit his second double of the game, advanced on a single by Damon and scored on a fly ball by Derek Jeter.
In the bottom half, Roberts led off with a double but was caught leaning too far off second and tagged out in a rundown. That proved costly, because Mora followed with a walk and took third on a double by Nick Markakis before Kevin Millar flied out.
