The Union suffered their second straight blowout loss in a road game Saturday night, falling 4-0 to the Montreal Impact in a game that was rarely close.

It took fewer than four minutes for the Union to fall behind. Lassi Lappalainen, who joined the Impact just this past Thursday on loan from Italian club Bologna, ran behind a ball-watching Ray Gaddis and rounded Andre Blake for an easy finish.

For most of the rest of the first half, the Union were the better team. But they conceded again in the 36th when Orji Okwonkwo finished off a textbook counter-attack with a thunderous shot from just inside the 18-yard box.

Whatever hope the Union had of a comeback disappeared barely 15 seconds into the second half when Montreal star Ignacio Piatti dispossessed Jack Elliott and sent Lappalainen off to the races on the left wing. With Gaddis nowhere in the picture, Lappalainen had plenty of time to look up and beat Blake to the far post.

Jim Curtin started making substitutions in the 49th minute, sending in Ilsinho for Brenden Aaronson and switching the Union’s lineup from a 4-4-2 to a 4-3-3. Seven minutes after that, Curtin shifted to a 3-5-2 by withdrawing left back Matt Real and sending in new striker Andrew Wooten.

Nothing worked. In fact, things only got worse. Okwonkwo scored Montreal’s fourth goal in the 66th on another counter-attack.

It likely isn’t a coincidence that the Union have conceded 10 goals in the four games that midfielder Jamiro Monteiro has missed with a sprained ankle.

The Union (11-7-6, 39 points) remain in first place in the Eastern Conference, but in a week visit a Wayne Rooney-led D.C. United team that is hot on their heels (9-6-9, 36 points). It will be the first of two games between the teams in August, and the Union also face a road trip to Chicago and a home game against second-place Atlanta (11-9-3, 36 points) before the month ends.

If Monteiro doesn’t return soon — and if his teammates don’t defend enough to make up for his absence — the Union’s time atop the standings might not last much longer.