09/15/2012 11:04 EDT | Updated 11/15/2012 05:12 EST

De Guzman scores in extra time to lead FC Dallas to 1-0 win over Whitecaps

FRISCO, Texas - The Vancouver Whitecaps were seconds away from ending a frustrating nosedive that has taken the team from a comfortable lead in the MLS playoff chase to one looking nervously over its shoulder.

Instead, things only got worse.

Canadian international Julian de Guzman blasted a stunning left-footed volley home in the final seconds of stoppage time Saturday as FC Dallas stunned the Whitecaps 1-0.

It was a defeat that left Vancouver (10-12-7) hanging on to the final playoff position in the Western Conference by one point over Dallas (9-12-9).

"Sometimes football is heartbreaking. Sometimes football is frustrating. Sometimes football is helpless," Whitecaps captain Jay DeMerit said. "That's what I think we feel here tonight. Anything that could have gone our way, didn't."

The Whitecaps have five games left — four at home — while FC Dallas has four to play, three of them on the road. But a lead that stood at 11 points a month ago is now down to the slimmest of margins thanks to five straight Vancouver losses, including four shutouts.

The Whitecaps' challenge now is more than merely playing better in the field, which they did Saturday. It's holding together their crumbling confidence as they head down the stretch.

"When you're down in the dumps, these things turn your way," DeMerit added. "So the overlying message is we've just got to dig ourselves out of this. There's only one thing that can get us out of this and that's belief we can, and belief things will turn. Because things like this can't keep happening."

And yet they do. In their last outing, a 2-0 loss to Los Angeles on Sept. 2, the Whitecaps were victimized by a pair of eye-popping goals by Juninho and David Beckham.

Those were topped by de Guzman's bomb off a corner kick that was cleared from the box. The midfielder from Toronto knocked the ball down with his chest and smashed it before it hit the ground, clearing two onrushing defenders.

Vancouver goalkeeper Brad Knighton, who had a strong outing in his second consecutive start in place veteran Joe Cannon, leaped high but couldn't quite reach it.

"It's a never-ending story," Knighton said. "The last two games I played there have been three wonder strikes, and this is probably going to win goal of the week as well. ... I saw enough of it.

"I just couldn't get there. I felt like I was in a good position but he hammered it off the volley and (into the) side netting."

The goal came at the end of seven minutes of stoppage time — the result of a broken corner flag and an injury to Dallas' George John — giving FC Dallas, desperate for a win to stay in the race, time to send waves of attackers at the Vancouver defence.

Dallas' Blas Perez scored just as regular time ran out but was called offside.

"It seemed like an eternity," Knighton said of the added time.

Knighton kept Vancouver in the game in the first half with a penalty kick save from David Ferreira before barely redirecting Brek Shea's blast over the goal.

The Whitecaps, who got their attack going after halftime, had two good chances to break the deadlock. The first came in the 67th minute when substitute Darren Mattocks got behind the defence but was forced away from the net by onrushing Dallas goalkeeper Kevin Hartman.

The other came in the 84th when John Thorrington got on the end of a Russell Teibert pass in close but was thwarted by Hartman.

"He was getting across his near post so I just thought I would kick it under him, back where it came from," Thorrington said. "I don't know what happened — it caught just enough of his leg as he was coming over and it popped up right to him.

"It's our choice how we respond to this result. Everybody gave everything into the game."