KANSAS CITY, Mo. -- Playoff teams are supposed to get healthy against the weaker teams in the league.

But that's just not happening for the slumping, injury-wracked Boston Red Sox, who suffered a 6-4 setback to the woeful Kansas City Royals last night at Kauffman Stadium.

The Sox didn't lose any ground to New York in the American League East because the Yankees blew a ninth-inning lead and lost at Chicago, so Boston's deficit still is two games back, three in the loss column.

Nevertheless, letting games get away against the Royals, who are saddled with the worst record in the majors, doesn't help the cause for the Red Sox, who have dropped three of four on this trip to the last-place Royals and Tampa Bay Devil Rays.

Boston, down by two runs entering the ninth and facing Ambiorix Burgos, who leads the majors with 10 blown saves, received a pair of walks in the ninth. But Burgos did not turn into Fausto Carmona, the Cleveland closer who blew two ninth-inning leads to the Red Sox at Fenway Park last week.

Burgos zipped a called third strike past Manny Ramirez, a questionable call by plate umpire Derryl Cousins, and then got Kevin Youkilis to tap into a game-ending forceout.

While the defeat, which included David Ortiz's 41st homer of the year and a 451-foot, two-run bomb by Wily Mo Pena, unofficially the 13th-longest homer ever hit at the stadium, was difficult to swallow, the performance of starter Jon Lester was disturbing.

Lester, who admittedly couldn't command any of his pitches, threw 24 pitches in the first inning and wasn't any more pitch-efficient thereafter. He was pulled after five innings, through which he labored for a total of 105 pitches, only 52 of which were strikes.

By the time Lester had hit the showers he had blown a 3-2 lead, which vanished on Emil Brown's two-run single in the fifth. Craig Hansen and Rudy Seanez each was nicked for a run, so the loss was pinned on Lester.

The rookie left-hander has made 12 starts since being promoted from Pawtucket. In exactly half of them, Lester has gone no more than five innings. In only two starts has he gone more than six innings.

Such performances are somewhat predictable and expected, but put a strain on the bullpen as the pennant race winds its way through the dogs days of summer.

"That's a lot of pitches for five innings," said Boston manager Terry Francona. "I'm not being critical of the kid. He's learning on the job and that's all part of it. As he goes on and gets more comfortable in the league, he'll trust his stuff. Those five-inning (outings) will turn into seven and eight. That's not happening now as much as we'd like.

"We know what he can do," added Francona. "We know he can go eight innings, but he's still learning how to do it."

One lesson Lester learned last night is that it's pretty difficult to pound the strike zone, even against a lowly Royals, when you can't find one pitch in your repertoire that you can throw for a strike.

"I was terrible all night," said Lester, who fell to 5-2, not having won since blanking the Royals on one hit in an eighth-inning five starts ago.

"I had trouble controlling all my pitches, the curve, changeup, fastball. I had no command of anything," said Lester. "I didn't have anything. Chalk it up as just one of those nights and I'll just go back out there in five days and try to do better."

Lester, who has shown a remarkable capacity to escape jams in his brief big-league experiences, stranded two baserunners in the first inning. He wasn't so fortunate in the second when two hits, including an RBI single by Angel Berroa and a sacrifice fly by David deJesus gave the Royals a 2-0 lead.

The Sox rallied for three runs off Kansas City starter Luke Hudson in the fourth, but three hits and a costly hit batsman plunged the Sox into a 4-3 hole.

Hansen surrendered a run in the sixth, thanks partly to his own throwing error. And seanez was ripped for a solo homer by Emil Brown in the seventh, negating the effect of Ortiz's homer in the top of the inning.

So it was another loss and another learning experience for Lester.

"I've been having good bullpens (between starts)," said Lester. "I just have to find a way to take those bullpens into the games. I'm not doing that right now."

And as a team, the Red Sox haven't been able to find a way to beat the lower echelon teams in the A.L., which has contributed to the fact that they are looking up at the Yankees in the division standings and the White Sox in the wild-card standings.

skrasner@projo.com / (401) 277-7340