Joe Willis makes a save in Wednesday’s loss to San Jose. (Ezra Shaw/GETTY IMAGES)

In perfect conditions, D.C. United’s road trip this week posed substantial challenges: two matches three time zones apart in 651 / 2 hours — its most difficult turnaround on the 34-game MLS calendar.

But then Coach Ben Olsen had to factor in a 5-3 loss at San Jose on Wednesday night, the club’s worst defensive performance in four years. He also had to come to terms with the injury-plagued back line that is still diluted for Saturday afternoon’s match at winless Toronto FC.

Adding to the stress, United’s flight from the Bay Area to Ontario was delayed two hours at the start and stuck for two hours at the end when thunderstorms prevented taxiing to the gate.

“It’s a tough stretch, but we’ve got to man up,” Olsen said. “We’ve got to find a way.”

The attack for United (4-3-3) has been purring at a productive pace with 10 goals in three matches and 18 overall (tied for second in the league). Dwayne De Rosario has rediscovered his 2011 form after a sluggish start and the collection of forwards has capitalized on scoring opportunities for the past month.

The defense, however, was in shambles against the Earthquakes, resulting in the end of United’s seven-game unbeaten streak.

“Away from home, three goals, you think that’s good enough to at least come away with a point, and we didn’t,” said De Rosario, who leads MLS in assists with seven. “We came away with nothing, and we’re disappointed about that part.”

Without Emiliano Dudar (hamstring), the back line lacked its central pillar and was under constant pressure against San Jose’s ambitious midfield and polished forwards. Dudar and fellow center backs Dejan Jakovic (ankle) and Ethan White (knee) will miss the Toronto game, forcing United to mix and match again.

Perry Kitchen’s move from defensive midfield to central defense Wednesday failed. “I don’t see Perry as a center back in this league,” Olsen said, “but sometimes you do what you have to do. We’re makeshift right now.”

Right back Robbie Russell, who provided central cover in previous games, is the top candidate to partner with Brandon McDonald, the only healthy center back. Chris Korb is the top candidate to fill Russell’s role and Kitchen seems set to return to his primary position.

“We’re scoring goals, and that’s fun and exciting,” Olsen said. “But we’ve got to close up shop and show greater commitment defensively.”

With a third game in eight days, Olsen might tweak the attack to include fresher players and rest banged-up regulars. The most intrigue swirls around the goalkeeping decision. Joe Willis has started the past nine matches after he inherited the job when Bill Hamid was away with the U.S. under-23 national team. Willis retained it with quality performances.

Willis, in his second season, wasn’t at his best last weekend against Houston and, although he didn’t make any horrible errors at San Jose, he could probably use a break. At the same time, Hamid needs playing time after sitting out seven matches since his return from U.S. duty.

Olsen said Friday morning he hadn’t decided which goalkeeper would start.

On the surface, United’s vulnerability with injuries and travel comes against the right opponent: Toronto hasn’t earned a point in seven matches, tying the 1999 Kansas City squad for the worst start in MLS history. Aron Winter’s crew has scored just six goals and has lost four times at BMO Field.

The Canadians were, however, the only MLS club to advance to the CONCACAF Champions League semifinals — the regional championship early this spring — and held a pair of leads at heavily favored Real Salt Lake last weekend before losing in stoppage time.

“We’re in no position to take anyone lightly after the performance we had” against San Jose, Olsen said. “Five goals was unacceptable. We’ve got to be better.”