Red Sox second baseman Dustin Pedroia throws to first base past the Blue Jays’ Marco Scutaro to complete a double play in the bottom of the sixth inning last night.

AP / Adrian Wyld

TORONTO — The plan was sound. Unfortunately, the execution left a little to be desired.

So as a result of a fat changeup that Red Sox reliever Manny Delcarmen fed Toronto Blue Jays designated hitter Frank Thomas, Boston wound up suffering a defeat at the Rogers Centre.

Thomas drilled a tiebreaking two-out, two-run double to left-center in the seventh, snapping a tie and sparking the Blue Jays to a 6-3 victory over the Sox before an Opening Night crowd of 50,171.

The double, on a 1-and-1 pitch, broke a 3-3 deadlock in what had been a scintillating scoreless pitcher’s duel between Boston’s Tim Wakefield and Toronto’s Shaun Marcum over the first 5 ½ innings. Pesky David Eckstein, who set up the pivotal seventh-inning rally by working an 11-pitch leadoff walk, delivered an insurance run with a two-out single off Delcarmen in the eighth.

The Sox managed only four hits, though one of them was a three-run homer by J.D. Drew off Marcum that tied the game in the top of the seventh.

While the offense sputtered, it was not a good night for the Sox’ bullpen, either.

Neither David Aardsma nor Javier Lopez, who are fighting to remain on the roster with the imminent arrivals of Josh Beckett and Mike Timlin from the disabled list, helped his cause. Aardsma issued the walk to Eckstein, the only batter he faced. And Lopez served up an 0-and-2 single off the glove of diving second baseman Dustin Pedroia to pinch hitter Shannon Stewart, the only batter he faced.

Delcarmen then took over against the meat of the Blue Jays’ order. And, with runners at first and second, the right-hander calmly retired Alex Rios and Vernon Wells on foul outs to first baseman Kevin Youkilis.

But Thomas stepped into a thigh-high changeup and cranked it to left-center, giving the Jays a 5-3 lead.

“He made good pitches to that point,” said Boston manager Terry Francona of Delcarmen. “That was a tough situation he was in. Manny’s got a great changeup. He was setting Frank up for a pitch, but maybe the reverse (happened).”

Delcarmen said the pregame scouting meeting planted the seeds for how he wanted to pitch the Big Hurt.

“We talked about it earlier. He’s a big guy who stands off the plate,” said Delcarmen. “You have to pitch him inside. My first two pitches I almost drilled him, but one of them was on the corner. Then I left the changeup up. On some guys that (location wouldn’t) be a bad pitch. But he’s so far off the plate that pitch was like middle-in to him. He got the (bat) head out and hit it in the gap.”

The ball floated to the plate almost in slow motion from Delcarmen’s vantage point. And Delcarmen could tell it was an accident waiting to happen.

“As soon as I let it go, I said, ‘Oh, no,’ ” said Delcarmen.

That wasn’t quite the same reaction Wakefield had when he watched his 1-and-0 knuckleball to Matt Stairs take a nice dip as it neared the plate in a 0-0 tie.

Stairs somehow got his bat to the ball and lined a homer over the right-field fence leading off the sixth inning, giving the Jays a 1-0 lead.

“It was a good pitch,” said Wakefield, who gave up six hits and three runs in six innings.

“It was one of those pitches that just ran into his bat. But you just have to tip your hat to him. He’s just a good hitter,” said Wakefield.

The knuckleballer didn’t have much luck the rest of the inning, as the Jays parlayed a couple of walks, a lost ball in the lights and a couple of hits into two more runs for a 3-0 lead. The damage could have been worse, too, but Wakefield got Gregg Zaun to hit into an inning-ending double play with the bases filled.

“Wake’s line score won’t make it look like he pitched as well as he did,” said Francona. His ball was moving all over the place in the strike zone.”

Marcum, meanwhile, was dominating the Sox’ offense, able to mix in changeups and sliders with his fastball. He kept Boston off-balance all night — until the seventh.

Armed with a 3-0 lead, a walk and a two-out broken bat single by Mike Lowell set up Drew for his clutch homer on a cutter that tied the game.

“He really had his way with us outside of J.D.,” said Francona of Marcum, who fanned eight and permitted only three hits. “He threw an outstanding changeup. He missed a lot of bats with it. He was great. He tied us in knots.”

Delcarmen tried to do the same thing with his changeup to Thomas, but didn’t quite have the same results.

“I was one pitch away,” said Delcarmen evenly. “That’s baseball. It’s early. I’ll get him tomorrow.”

skrasner@projo.com