WASHINGTON -- Although Nationals shortstop Cristian Guzman is back action, he is still playing with a sore left thumb, according to manager Manny Acta.

Guzman said he hurt his thumb while playing against the Reds during the first week in July and aggravated it near the end of the month against the Giants. He ended up missing 12 starts before returning to action on Aug. 7 against the Rockies.

Guzman is now playing with a pad to help protect the thumb.

"The thumb is not 100 percent -- I have to give the guy a lot of credit [for staying in the lineup]," Acta said. "We are monitoring the thumb and plan to give him a day off here and there. He is using a different padding in the thumb."

Guzman finds himself in a 5-for-29 slump as his overall batting average dipped to .294. He is among the league leaders in hits, however, with 136.

"The thumb is not stopping him from playing and he is doing it for the team," Acta said.

Pitching matchup
WSH: RHP Collin Balester (2-4, 4.66 ERA)
Balester turned in another good performance on Friday against the Brewers, allowing just four runs (three earned). He went five innings and struck out four, but the Nationals were shut down by Milwaukee hurler CC Sabathia and Balester picked up the loss, his fourth of the year.

NYM: LHP Oliver Perez (8-7, 3.90 ERA)
Perez threw seven scoreless innings Friday, holding the Marlins to two hits and striking out eight. His slider hit every spot he aimed for, starting it over the plate and having it slide in toward right-handed batters, and Perez's fastball showed a tremendous amount of life at 95 mph. But it was also a taxing outing, robbing Perez's arm of 120 pitches. With the win, he moved to 7-0 against winning teams, but now he faces the Nationals, who are last in the National League East. On April 24, his first and only outing against Washington this year, he allowed five runs in 5 2/3 innings.

Tidbits
In his 17 quality starts, John Lannan is 6-5 with a 1.98 ERA. ... Lastings Milledge is on a 14-game hitting streak. He is hitting .375 (21-for-56) during that span.

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Up next
• Friday: Nationals (Tim Redding, 8-7, 4.61) vs. Rockies (Jorge De La Rosa, 5-6, 6.28), 7:35 p.m. ET
• Saturday: Nationals (John Lannan, 6-11, 3.40) vs. Rockies (Livan Hernandez, 10-9, 5.94), 7:10 p.m. ET
• Sunday: Nationals (Odalis Perez, 5-8, 4.12) vs. Rockies (Ubaldo Jimenez, 8-11, 3.94), 1:35 p.m. ET