CHICAGO -- There's a recurring theme regarding the Cubs since the All-Star break: They're having a tough time beating winning teams.

On Thursday, the defending World Series champion Philadelphia Phillies won, 6-1, and the Cubs dropped to 3-10 against teams with winning records since the break.

"[Winning teams] seem to have no problem beating us," Cubs starter Ryan Dempster said. "I know everyone wants to search for answers, including ourselves at times. We want to try to figure out if we're not playing smart enough, we're not playing hard enough, we're not executing enough.

"Sometimes when you try to search for so many answers, you end up doing a little too much. We need to go back to the basics and just attack one inning at a time, one pitch at a time and get back up and win a ballgame tomorrow."

The good news is they're 12-2 against ballclubs with sub-.500 records, and they play the Pirates and Padres next. If they take advantage of the next six games, the Cubs should stay in the National League Central race, in which they trail the first-place Cardinals, who were idle Thursday, by 4 1/2 games.

Ryan Howard smacked a three-run homer and Pedro Feliz hit a solo shot to help Cliff Lee win his sixth straight start and complete a sweep. Chicago now has lost seven of its last eight games.

"We're not playing like a good team right now," Chicago's Derrek Lee said. "It's just look in the mirror and get better."

Dempster (6-6) struck out eight but took the loss, serving up both homers to the powerful Phillies, who lead the NL with 157 home runs.

"They made me pay for some mistakes I made," Dempster said.

Dempster retired nine of the first 10 batters he faced. Shane Victorino then singled to lead off the fourth -- and avoided having any beverages soak his uniform -- and Chase Utley walked to set up Howard's homer, his 27th. Two outs later, Feliz smacked the first pitch from Dempster into the left-field seats for a 4-0 lead. They were the 16th and 17th off Dempster, making his 21st start. In 33 games last year, he served up 14 home runs.

It was one bad inning for Dempster.

"The one pitch to Howard specifically," Cubs manager Lou Piniella said. "He tried to backdoor a slider, and it stayed up and got in the wind and went out."

The home run snapped a 57 at-bat homerless streak for Howard, which tied a career high.

"It feels nice to homer when you haven't homered in a while," Howard said. "When you can get hits like that to kind of get your team off to a good start, it's always a good feeling."

Not as far as the Cubs were concerned.

"I put us behind the eight ball by giving up a big home run right there," Dempster said. "It wasn't that bad a pitch, but when you're facing a guy like [Howard], he can hit the ball a long way, and he got it up in the air and got it out for a three-run homer."

That's all Cliff Lee needed. The left-hander has looked more like a reigning Cy Young winner since the Phillies acquired him July 29, and he struck out eight over eight innings. He faced the Cubs on June 19 in an Interleague game, but did not get a decision. In that game, the Cubs scored three runs on six hits in Lee's seven innings, en route to erasing a 7-0 deficit and pulling out an 8-7 win over the Tribe.

On Thursday, they couldn't muster much until the fifth. Jeff Baker doubled to open the inning and scored one batter later on Ryan Theriot's single for his career-high 46th RBI. Theriot's previous high was 45, set in 2007.

In the three games against the Phillies, the Cubs were outscored, 22-9. They batted .229.

"Let's hope we turn around our fortunes, and quickly," Piniella said. "It's been a struggle."

"We've had some good teams we've played lately -- Florida and then Colorado and then these guys," Theriot said. "It's been a good test for us. We haven't won the games we'd like to win, but this is what it's going to be like come October if we're lucky enough to get there."

October? The Cubs need to get through August first. They still have to play the NL West-leading Dodgers this month.

"Baseball has its ups and downs, and we've had some downs here and we need to just get on a hot streak," Baker said. "I've seen it happen with a lot less talented teams than what's in this clubhouse. That's no knock on the other teams. We've got the ability to get hot. We just have to start small and get it going."

They don't need a motivational speech.

"We're all grown men, and we have to look ourselves in the mirror and say, 'Let's get better,'" Derrek Lee said. "There's only so much talking you can do. This is the middle of August, and we all know the job we have to do. We're not where we want to be right now, but we have five or six weeks to go, and we're still in it."

The Cubs should get Aramis Ramirez back on Friday. Ted Lilly is slated to be activated from the disabled list Monday and Carlos Zambrano isn't far behind. Being at full strength will help. What else?

"Play better," Lee said. "There's no magic formula. You have to go out and get the job done."