BALTIMORE – First, Bartolo Colon lost his shutout.

Then, the A's lost a heartbreaker.

The Baltimore Orioles erased a two-run deficit in the bottom of the ninth inning and sank the A's 5-2 Sunday, dealing Oakland its biggest punch-in-the-gut loss of 2012.

Wilson Betemit's walk-off three-run homer off Grant Balfour ended things, but the winning rally began with two soft infield hits off Colon.

That's what had to sting most as the A's were in position to win the three-game series at Camden Yards before heading to Boston.

"It stinks," A's outfielder Seth Smith said. "But we'll get up tomorrow, go to the ballpark and try to win a game."

Colon turned in another excellent effort, holding the Orioles to five hits over the first eight innings and doing it primarily with his fastball. The A's led 2-0 when he took the mound in the ninth looking for his 10th career shutout.

J.J. Hardy hit a ball up the middle that A's second baseman Eric Sogard made a great backhand play on. He made an off-balance throw to first base that Daric Barton couldn't make the scoop on.

After Nick Markakis struck out, Adam Jones hit a tapper near the mound. Colon fielded the ball and fired a throw to first that was in the dirt. This one got by Barton to allow the tying runs to advance to second and third.

That ended Colon's day, and Balfour, the A's closer, inherited one mighty tough scenario.

It's debatable whether Barton should have snagged Colon's throw or at least kept the ball in front of him. But Sogard's soft one-hop throw appeared catchable.

Barton, who pinch hit for Kila Ka'aihue in the top of the ninth, said both balls caught him between hops. But he took responsibility.

"If they put me in for defensive purposes, I probably should have those," he said.

With one out, Balfour got ahead of Matt Wieters 1-2 and tried to bounce a curve in the dirt. Wieters roped a two-run double off the left-field wall that tied the score, accounting for Balfour's second blown save in five days.

"That's a tough position right there," Balfour said. "A base hit ties the game, and I was really trying to go for a strikeout. It wasn't like I left it up, but I left it up enough for him to get too good of a swing on it."

After an intentional walk to Chris Davis put runners on first and second, Balfour fell behind Betemit 3-1 and came in with a fastball. Betemit knocked it over the wall in right-center to unleash a celebration for an announced crowd of 31,793.

Notes – Free-agent third baseman Brandon Inge is set to join the A's, a source confirmed.

The sides are nearing a contract, though A's officials are not commenting. Inge, who turns 35 in May, must pass a physical before any deal is official.

• A's right fielder Josh Reddick, obtained from Boston over the winter in the Andrew Bailey trade, is looking forward to his first game back at Fenway Park today.

• Jemile Weeks got his first day off of the season, which came at a good time considering he's hitting .187 with a .253 on-base percentage.

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