WASHINGTON (Ticker) -- Everything appears to be going the Washington Nationals ' way lately, and now they have a record to back that up.

Vinny Castilla homered and drove in three runs and Brian Schneider added a two-run shot as the Nationals established a franchise record for wins in June with a 7-5 victory over the Pittsburgh Pirates .

Improving to 20-6 after its fourth series sweep of the month, Washington surpassed the previous franchise mark of 19-8 set by the Montreal Expos in 1994.

"That's a tremendous year, or month, I'm sorry," Nationals manager Frank Robinson said with a smile. "After the last three years, it seems like a year. That's a tremendous month and the players deserve an awful lot of credit for the way they have performed and the way they have handled things. They just keep going out and doing the job."

Closer Chad Cordero , who nailed down his major league-leading 28th save in the ninth inning despite giving up a single and double to the first two batters he faced, also entered the record book.

"I thought he had gotten over that in the last three or four outings, but I guess he's just not going to let me get comfortable," Robinson said. "That's the way it goes, but he's not fazed and he finds a way to get out of it."

"I'm kind of getting used to it because I've been thrown into it so many times," Cordero said. "I was getting a little worried when they were at second and third with no outs, but I learn something new every day. I'm still trying to learn what kind of pitcher I am."

A day after he surpassed Mel Rojas for the franchise record by converting his 24th consecutive save opportunity, the 23-year-old tied a major league record with 15 saves in a month, joining St. Louis' Lee Smith in 1993 and the New York Yankees ' John Wetteland in 1996. All three pitchers accomplished the feat in June.

"I'll go out there every day if they want me to do it," Cordero said. "I'm not worried about being overworked."

Robinson chuckled when asked if Cordero is on a roll.

"That may be the understatement of the year," Robinson said. "He's like an avalanche right now, picking up speed. He's just doing the job. I don't know when to stop pushing the button, I really don't."

Esteban Loaiza (4-5) got off to a strong start for the Nationals, holding the Pirates without a hit over the first 4 2/3 innings. He did not get an out in the sixth, allowing four runs and five hits.

"He had good stuff and then all of a sudden he lost a little bit of his location," Robinson said. "With the heat out there and the weather, you never know when maybe someone's had a little bit (too much) because he had a low pitch count and he was making it look easy. I would take into consideration the weather taking a little something out of him, but he had one of these coming."

Loaiza threw 47 of his 69 pitches for strikes. He had averaged 96.8 pitches in his previous four starts.

Castilla gave Washington a 4-0 lead in the second with a two-run single and hit his sixth homer in the seventh for a 7-4 advantage.

"His performance hasn't been tremendous of late, but he's gotten an awful lot of big hits for us and driven in some big runs," Robinson said. "Today is another case of it - three RBI and a big home run. But the one thing about Vinny, it hasn't affected his defense. This is why you want to keep him in the lineup because he's capable of doing it at any time."

"This is what winning teams do - always find a way to win," Castilla said. "We've been doing that since the season started. Since spring training, I've always said we have a pretty solid ballclub and we show up every day ready to play. We've got a lot of talent here."

Pittsburgh starter Kip Wells (5-8) struggled with control problems, giving up four runs, four hits and four walks in two innings, his shortest outing of the season.

"It was a tough outing for him," Pirates manager Lloyd McClendon said. "I still think that Kip is going to be a key part of our success. I think he's going to turn it around and pitch the way we know he can."

The Pirates have dropped 15 of their last 20 road games and five of six overall.

McClendon was ejected for the fourth time this season, arguing balls and strikes in the second. Wells issued three walks in the frame, leading to three runs behind an RBI single by Jose Guillen and the bases-loaded hit by Castilla.

The Pirates moved within 6-4 in the sixth when Daryle Ward hit a blooper over the head of Castilla at third, scoring Bobby Hill and Rob Mackowiak .

The Nationals may have lost shortstop Cristian Guzman for a few games after he pulled his left hamstring running to first in the eighth.

"We're just going to have to take a look at him tomorrow and see how he is," Robinson said. "Hopefully it will only be a couple days. I believe we'll have him in the Chicago series."