The Blue Jays’ A.J. Burnett, delivering a pitch in last night’s game, held the Red Sox in check until the fifth inning.

AP / J.P. Moczulski

TORONTO –– One-run victories on the road have been hard to come by for the Red Sox, and apparently they’re not about to get any easier in the final weekend of road play for the team.

The Sox increased the degree of difficulty for themselves in the ninth inning last night when closer Jonathan Papelbon fumbled a dribbler by Adam Lind, then made matters worse by skipping an off-balance throw past first to enable Lind to take second, putting the potential tying run in scoring position with none out.

But Papelbon buckled down and retired the next three hitters, preserving a hard-fought and critical 4-3 victory over the Toronto Blue Jays.

“Good win,” concluded Sean Casey, who delivered a key two-run double in a three-run fifth off starter A.J. Burnett. “We needed that.”

The win, coupled with the loss by Minnesota, sliced the Red Sox’ magic number in half — from four to two. The Sox can clinch a playoff spot today with a win, a Yankee loss and a loss by either Chicago or Minnesota.

Meanwhile, the Sox kept within a game and a half of first-place Tampa Bay in the race for the A.L. East title.

It was just the fourth one-run win of the season on the road for the Sox, and just the second since April 1. Both since then have come at Rogers Centre, against these Blue Jays.

The Sox snapped a 3-3 tie in the bottom of the eighth when Jason Varitek’s slow-rolling fielder’s choice scored Jason Bay from third with the go-ahead run.

“A nice, soft ground ball to the right place,” said a smiling, satisfied Varitek.

Papelbon then nailed down his 39th save of the season, capping three scoreless innings from the Boston bullpen in which four relievers –– including Javier Lopez, Manny Delcarmen and Hideki Okajima –– allowed just two baserunners.

Delcarmen earned the win, his first since Aug. 31, 2006 –– also against Toronto. Until last night, he had made 122 appearances without collecting a victory.

With one more save, Papelbon can become the fifth Red Sox pitcher to notch a 40-save season, following Tom Gordon, Derek Lowe, Ugueth Urbina and Jeff Reardon.

Paul Byrd, facing the Blue Jays for the fifth time in his last eight starts, went six innings and allowed three runs on six hits.

“He gives us six (innings), and that gives us a chance to win,” said manager Terry Francona. “Sometimes that’s good enough. It worked out pretty well.”

Byrd gave up three straight doubles in the second as Toronto got out to a 2-0 lead. He then retired eight in a row before yielding a run-scoring double to Marco Scutaro in the bottom of the fifth, after the Sox had struck for three runs off Burnett.

“That was frustrating,” said Byrd of the fifth-inning run, “but the team eased my pain later on (by scoring the go-ahead run in the eighth).”

Knowing the Blue Jays were all too familiar with him, having faced him five times in the last seven weeks, Byrd changed his approach by pitching backward –– throwing breaking balls early in the count to get ahead before reverting to his fastball –– and the method was largely successful.

The Sox had little success against Burnett, except for the fifth, when they erased the Blue Jays’ 2-0 lead and did so with two out.

Varitek cracked a double down the left-field line and advanced to third when Jacoby Ellsbury hit a slow roller that Burnett seemed disinterested in fielding.

Ellsbury was then picked off first, but the inning continued when Dustin Pedroia hit a rocket at Scutaro in the hole. Varitek broke for the plate, but when Scutaro went home with his throw, Varitek quickly retreated to third as Pedroia reached on the fielder’s choice.

A single up the middle by Kevin Youkilis scored Varitek and sent Pedroia to third, and both scored when Casey pulled a double into the right-field corner.

“I was just trying to get a pitch I could do something with,” said Casey, whose two RBI matched his production since Aug. 1, “and when I got ahead, 2-and-0, I was hunting for a fastball. If you can get Burnett in trouble you’ve got to take advantage of it, because otherwise he can shut you down.”

“Any time you’re facing Burnett,” added Francona, “it’s tough. His stuff is so good. You’ve got to scrap for anything you can get, and that’s what we did.”

smcadam@projo.com