Boston ? A comeback victory kept the Boston Red Sox in first place. Staying there could be tougher if Tim Wakefield is sidelined.

A back injury ended the knuckleballer’s outing after four innings Monday night, and Boston rallied from a four-run deficit for a 5-4 victory over the Kansas City Royals capped by Manny Ramirez’s sacrifice fly in the eighth inning.

Wakefield, whose start was pushed back a day so he could rest his back, will undergo tests on his strained upper back today, and manager Terry Francona said “I guess I’m still hoping” he doesn’t go on the disabled list.

Two other starters, Matt Clement and David Wells, already are on the disabled list.

The first-place Red Sox stayed one-half game in front of New York in the AL East as the Yankees beat Seattle, 4-2, on Monday.

The Red Sox, who had lost four of five, hoped to stop their slide as they began a four-game series against baseball’s worst team. But Luke Hudson shut them out for six innings while Kansas City took a 4-0 lead.

Boston tied the game in the seventh on Coco Crisp’s RBI single and Doug Mirabelli’s three-run homer before pinch-runner Willie Harris scored the winning run on Ramirez’s fly ball to medium left field.

Boston's Willie Harris slides into home with what proves to be the winning run on a sacrifice fly by Manny Ramirez in the eighth inning. The run ahead of the tag of Royals catcher John Buck, right, lifted the Red Sox to a 5-4 victory Monday in Boston.

“We just didn’t do much offensively for a while,” Francona said. “Once Dougie hits that ball, the whole complexion of the game changes.”

Mike Timlin (5-0) pitched a perfect eighth, and Jonathan Papelbon worked the ninth for his 27th save in 30 opportunities. Joel Peralta (1-2) was the loser as the Royals lost for the sixth time in seven games.

“We just can’t seem to make a pitch when we need to,” Kansas City manager Buddy Bell said. Peralta “has been throwing good for us. He went 3-2 on Mirabelli. He had to come in there.”

Hudson allowed just two runners to reach second base in the first six innings, one on an error that broke Mark Grudzielanek’s 95-game errorless streak, 18 last year with St. Louis and 77 this year with Kansas City, a club record.

The Royals had taken a 3-0 lead in the second and made it 4-0 in the sixth against Manny Delcarmen.

Wakefield hit Emil Brown with a pitch then retired the next two batters. But Mark Teahen singled, and Joey Gathright walked, loading the bases. John Buck walked, forcing in the first run, and David DeJesus followed with a two-run single.

Delcarmen pitched a scoreless fifth then allowed a run in the sixth when Teahen singled, Gathright walked and both advanced on Buck’s sacrifice bunt. Teahen then scored on DeJesus’ groundout.

Hudson said he was relying on “fastballs. They’re a good hitting bacllclub. You have to get ahead of them” in the count.

Boston tied it in the seventh when singles by Ramirez, Mike Lowell and Crisp produced one run and chased Hudson with one out. Peralta then threw a 3-1 pitch that appeared to be a ball, and Mirabelli took four steps toward first base before home plate umpire Jim Joyce called it a strike.

Mirabelli lined the next pitch into the seats in left for his third homer.