ST. LOUIS -- Mental mistakes, walks and a passed ball proved to be costly for the Nationals, who lost to the Cardinals, 5-4, at Busch Stadium on Saturday afternoon.

Washington has lost three consecutive games to even its record at 3-3.

Left-hander Matt Chico lasted six innings and gave up four of the five runs. Bad mechanics had nothing to do with giving up the runs. He made a couple of mental mistakes, according to pitching coach Randy St. Claire.

For whatever reason, Chico had problems with the bottom of the Cardinals' batting order. In the second inning, Adam Wainwright and Cesar Izturis, batting eighth and ninth, respectively, had RBI singles, while Yadier Molina, a career .248 hitter, drove in two runs with a single in the next inning.

Chico didn't have any problems with meat of the order -- Brian Barton, Rick Ankiel, Albert Pujols, Troy Glaus and Ryan Ludwick -- which went a combined 2-for-14. The rest of the order -- Molina, Adam Kennedy, Wainwright and Izturis -- went 5-for-10.

"I thought he threw the ball OK, but he made mistakes that hurt him," St. Claire said. "The pitcher hurt him, falling behind to the bottom of the order. Those are the guys that hurt -- the little guys, not the big guys.

"He made a mistake to Kennedy -- hanging breaking ball. He fell behind Izturis. He threw a fastball down the middle. He fell behind the pitcher. He threw a fastball down the middle. Those guys you have to put in your back pocket. Those are the guys you have to get out. ... [The pitches] were more mental mistakes than physical."

Chico settled down and was able shut out the Cardinals the next three innings. The good news wa that he walked only two batters. For the season, he has walked only three in 11 1/3 innings.

"I had to calm down, Chico said. "I couldn't take the four runs back. I was trying to keep the team in the game."

Wainwright pitched eight solid innings and gave up two runs on eight hits. Washington had Wainwright on the ropes in the fourth, but only scored one run. With one out, Ryan Zimmerman scored on Nick Johnson's single. Austin Kearns followed and hit a hard grounder up the middle. Kennedy made a spectacular stop and threw to Izturis to force out Johnson.

"It was a great play. It stopped our momentum after that," manager Manny Acta said.

Ronnie Belliard then singled to left and Felipe Lopez walked to load the bases. Jesus Flores followed and grounded out to end the fourth.

The Nationals added another run off Wainwright in the eight inning, when Johnson hit a solo homer. It was his first home run since Sept. 19, 2006, against the Braves.

Lopez felt that Washington missed several opportunities to score off Wainwright. In fact, Lopez went so far as to say that Braden Looper, Friday's winning pitcher, was much tougher.

"We were way too aggressive [on Saturday]," Lopez said. "People were chasing that slow curveball. We were hitting the balls hard at people, too."

The Cardinals got the run back in the bottom of the eighth and it came back to haunt the Nationals.

Reliever Jesus Colome was able to get two quick outs, but he walked the next two hitters. Ray King came on to stop the bleeding, but he walked Izturis to load the bases.

With Skip Schumaker at the plate, King threw a 1-1 fastball that went by Flores for a passed ball. Kennedy ended up scoring on the play.

King and Flores agreed to go with a two-seam fastball on the inside part of the plate, but the ball tailed on the outside part, and Flores didn't see it coming.

"It was hard for me to stop it," Flores said. "Unfortunately, they scored [the go-ahead run]."

King blamed himself for the pitch going by Flores.

"It got away from me," King said. "I didn't give Flores a chance to get it. ... We would probably be playing right now."

Flores belted a two-run shot in the ninth off right-hander Anthony Reyes to make it a one-run game. As he was running the bases, Flores was thinking about the passed ball.

"It came back to mind. We could be in a tie game," Flores said.