John Lannan throws a season-high 115 pitches and ties his season-high for walks. (Jonathan Newton/The Washington post)

Thursday afternoon, submerged in thick, hazy heat, the Washington Nationals’ 2011 season continued its drift toward irrelevance. Having already fallen from contention, the Nationals, by playing games like their 5-2 loss to the Florida Marlins, are now simply trying to turn their season back around.

Before 24,153 at Nationals Park, the Nationals endured a sweep by the Marlins and extended their losing streak to five games, matching their longest skid of the season. Another lackluster offensive showing collided with an uneven performance by starter John Lannan as the Nationals dropped to 9-16 under Manager Davey Johnson and 49-55 overall, their furthest from .500 since mid-June.

The Nationals recently have abandoned the crisp, opportunistic baseball that lifted them to a stretch of 13 wins in the 15 games prior to Johnson’s arrival. Part of that might be regressing to the mean in close games — the Nationals won six straight one-run games before Johnson took over, and now they’ve lost their last seven. But the Nationals have hardly been competitive in their past four games, and a lack of concentration is at least a partial cause.

“Up until this point, we’ve been doing the little things to help us win games, help us stay in games,” right fielder Jayson Werth said. “I’d say the last few nights, for sure, it seems like fundamentally we haven’t been that sound. That’s really not that hard to get back on track. That’s just focus and playing the game the right way. Just chalk that up to a bad stretch, but realistically, we’ve got to play better baseball. The last couple nights, I think we might have just lost focus a little bit.”

Werth could not pinpoint the reason behind the Nationals’ recent lapse, but he hazarded one guess. The trade deadline looms Sunday, and as the Nationals’ front office has actively sought trades about half the clubhouse has seen their name show up in trade rumors.

“That could be it,” Werth said. “A lot of these guys are pretty young. They haven’t been through this. It’s not tough to turn on your computer and find your name somewhere. I went through it last year, and it is hard to play when that stuff’s out there.”

Thursday afternoon, neither team acquitted itself all that well, owing largely to 10 combined walks by the starting pitchers. Marlins starter Brad Hand lasted only 32 / 3 innings, during which time he managed to walk six batters. He so exasperated Manager Jack McKeon that he was pulled in the fourth inning, with the count 1-0 in the middle of an at-bat.

But the Marlins “took advantage more than we did” of their scoring chances, Johnson said. Making his Nationals debut, Jonny Gomes, acquired Tuesday in a trade with the Cincinnati Reds, went 0 for 3, killing both the Nationals’ best chance to seize control and their last chance to sneak back into the game.

In the third inning, after Werth’s bloop single tied the game at 1 and kept the bases loaded with one out, Gomes grounded into a 4-6-3 double play. In the seventh, after Werth delivered a line-drive RBI single, Gomes struck out with two down and runners on the corners.

The Nationals bungled another chance in the fourth inning, when Ian Desmond and Jerry Hairston stood on second and first with two outs, right after Hand departed. Johnson flashed a sign to let the runners know they could steal if a perfect opportunity arose. Somehow, through third base coach Bo Porter, Desmond and Hairston thought Johnson wanted a double steal. John Buck threw Desmond out to end the inning.

“It was a missed sign,” Johnson said. “Things aren’t just kind of going our way.”

Said Desmond: “The offense is a little bit slow right now. We’re trying to put a little pressure on people, play aggressive baseball. It didn’t work out.”

The Nationals drew seven walks but managed only seven hits, six of them coming from Ryan Zimmerman and Werth. Zimmerman went 4 for 5, his second consecutive game with at least three hits. Zimmerman is 13 for 27 in his last six games, having raised his average from .240 to .276 over that span. Werth went 2 for 4 and drove in both of the Nationals’ runs, the second RBI single coming on a 3-2 fastball by Edward Mujica in the seventh after he had fouled off five straight pitches.

After a streak of 12 starts without allowing more than four earned runs, Lannan gave up four in 52 / 3 innings on five hits and four walks. In his last start, Lannan allowed one run in 61 / 3 innings, but chastised himself for allowing three walks. Thursday, he ratcheted his pitch count with consistent wildness, throwing a season-high 115 pitches and tying his season-high for walks. Lannan walked the leadoff hitter in three straight innings, from the third to the fifth.

“It’s unacceptable,” Lannan said. “That’s pretty much it. It’s just getting out of my own head, just going out there and throwing it. I don’t know what’s going on, but I’ve just got to go out there to the bullpen, throw the sinker and get it back.”

Chien-Ming Wang will join the Nationals’ rotation Friday night by making his first start of the season, and now may be the time for some kind of change among the starters, who have allowed 22 runs in 251 / 3 innings. It is the kind of stretch they had avoided all season. With their season reaching one of its lowest points, and with the trade deadline around the corner, the question now is how the Nationals will respond.

“You can’t have a meeting about it or anything like that,” Werth said. “We need to come out focused, ready to play, ready to win. Be tenacious. It’s easy to do. We just need to refocus a little but.”