Heading into the Fourth of July weekend, Seattle had a 10-point lead in the hunt for its first Supporter’s Shield. It had the inside track for home-field advantage throughout the Major League Soccer playoffs, and reinforcements were on their way with World Cup representatives Clint Dempsey and DeAndre Yedlin set to return from Brazil.

The Sounders have lost three of their four MLS matches since, including their last two.

“I think we got a little too comfortable in our positions and the way we were playing,” forward Chad Barrett said Thursday after training.

“But two losses will wake anybody up.”

With one of the most challenging stretches of their season beginning Sunday night against Houston, the Sounders will be hoping that cold-water splash of reality has an effect.

The attacking chemistry that characterized the early part of the schedule has showed itself only sporadically in recent matches.

The short break for the MLS All-Star Game, in which four Sounders made an appearance, didn’t help matters. Nor did the fact that while three of them returned to training this week, Yedlin flew overseas to meet with an unidentified European club ahead of a potential transfer.

“We had some rhythm already, in some past games, but then some players had to go,” midfielder Marco Pappa said.

“They’re great soccer players, so they can come back and play with no problem. But it’s just the rhythm.”

Injuries have also hurt cohesion, especially in defense.

Brad Evans returned for the one-goal loss in San Jose after missing the 3-0 defeat to the Galaxy at home. Djimi Traore hasn’t made an appearance since late May, though he went through full training this week.

Chad Marshall’s fender-bender turned into a two-game absence that finally looks set to end Sunday.

“I hope so,” fellow defender Jalil Anibaba said. “Obviously, we need him. When he’s back there, we’re real solid.”

Without him, the gap in the standings has begun to close.

Sporting Kansas City has overtaken the Sounders in the Supporter’s Shield hunt, though Seattle does have two games in hand. Real Salt Lake and L.A. are coming on strong in the West.

Now comes a stretch that will see Seattle play five league games and an Open Cup semifinal all before September. It includes road trips to Salt Lake and Portland and begins with three matches in six days.

“What we try to do is approach each game individually,” Sounders coach Sigi Schmid said. “We’ve mapped out lineups for all three games in our minds.

“But in general, game No. 1 is the most important one.”

Game No. 1, the first of six in 20 days, is Sunday at CenturyLink. Kickoff is 7:30 p.m.