PITTSBURGH -- This time, the unraveling came in the fourth inning.

Blame the command. Blame some bad luck. Blame whatever you wish. Doing so won't change the results, nor is it likely to make Paul Maholm's season any less defined by the maddening inconsistency that has plagued it since mid-June.

On Saturday, the Pirates' 9-2 loss to the Nationals ended another frustrating night for Maholm, who lasted only 4 1/3 innings in front of 30,263 at PNC Park. In the process, the left-hander allowed seven earned runs.

"It's frustrating," Maholm said afterward, alluding both to Saturday and his string of inconsistent results. "Nobody is more frustrated than me."

The outing started out just fine for Maholm, who through three innings did not allow a hit. But -- as has been the case in too many of his 2010 starts -- anything good that was being built up crumbled in an inning's span. This time, it was the Nationals' five-run fourth that sent Maholm spiraling.

Washington banged out six singles in the frame. The authority in which those balls were hit varied drastically, but the result was nonetheless game-changing.

The inning began with Jose Tabata unable to corral a sinking hit in shallow left. A walk and bunt single later, catcher Ivan Rodriguez crushed a fastball off the right-field scoreboard. Lastings Milledge gave chase to the hit, but was going back looking over his left shoulder only to have the ball bounce low to his right and away from him.

"It was hit hard," Milledge said. "I thought I had a chance because usually those balls hang up a little bit. I thought I had a chance of getting it. At the last minute, I ran out of room."

Rodriguez's hit scored two.

"It's a tough play," added manager John Russell. "He's got to go all the way back to the wall and time it."

A sacrifice fly and two more hits -- including a poke into left by former Pirate Nyjer Morgan -- finished the damage. By the end of the inning, the Nationals had sent 10 hitters to the plate.

"Not good to allow it to get out of hand," Maholm said. "It's about as frustrating as it can get right now. But I'm going to have to figure it out. It's disappointing to me, and it's disappointing to a lot of people. But I'll come in tomorrow and try and figure it out."

Being on the wrong end of a big inning is something Maholm has become plenty familiar with recently. Dating back to June 18, Maholm has allowed four or more runs in a single inning in nine different starts. In five of those nine instances, an opponent has scored at least five in one frame.

That explains why Maholm has been unable to get through the fifth in five of those 15 outings. The left-hander's ERA has jumped from 3.63 to 5.43 during that span, despite some outings -- like Saturday's -- where Maholm felt he was more a victim of lousy luck than terrible command.

"You can sum it up pretty quick right there," Maholm said when asked if the fourth served as a microcosm of his season. "I expect a lot out of myself. Other people expect a lot. I haven't pitched the way I'm supposed to. I just take this as a learning experience. It definitely can't get any worse. I'll continue to grind it out for the rest of the season, and get it back to normal."

Maholm (7-14) pitched to three more hitters in the fifth, the last of which was Rodriguez. Capping his three-hit night, Rodriguez clubbed a two-run homer to chase Maholm from the game.

"Consistency is the biggest key," Russell said, speaking of Maholm. "It's just being able to go out and being able to execute and maintaining that. He's struggled with that. Hopefully he really locks it in this last month and goes away with a really good feeling, knowing that he's been through some really tough times, but can bounce back from that.

"If we could pinpoint the exact switch that we could flip, that would be great."

Washington's early lead gave starter John Lannan more than he needed to pick up his fifth win in his past six outings. The Pirates didn't get a hit off Lannan until the fourth and finished with only five hits against him in seven innings.

The only run scored off Lannan came via Andrew McCutchen's 13th home run of the season, a solo shot with one out in the fifth. The Nationals committed three errors behind their starter, but the Pirates couldn't capitalize on those either.

"Lannan was outstanding," Nationals acting manager John McLaren said. "He just threw strikes and kept them off-balance with location."

The Pirates' only other significant sign of life came in the eighth. Two singles sandwiched around an out brought Ronny Cedeno to the plate, and the shortstop delivered an RBI double to left. Two runs tried to score on the hit, but Milledge -- being waved the entire time by third-base coach Tony Beasley -- was thrown out easily at home.

"Down that big, that run is not going to be that big of a deal for us," Russell said, though noting he would have preferred a stop sign go up. "Talk about one play or one run, we got beat, 9-2. A lot of the damage was done early."

Second baseman Neil Walker finished the game 1-for-4, with his two-out double in the fifth extending his hitting streak to a career-high 11 games. The hit was Walker's 100th of the season, making the second baseman the first Pittsburgh rookie switch-hitter with 100 hits in a season in 28 years.