The Union's defensive miscues are becoming a trend. For the third straight Major League Soccer game, the Union allowed three goals Saturday night.
Unlike in Wednesday's 4-3 win over the Chicago Fire, this time the Union couldn't survive.
After taking a 1-0 lead, the Union allowed the next three in a 3-2 loss to the Vancouver Whitecaps before 17,225 fans at Talen Energy Stadium.
The Union (7-5-5, 26 points) remained in first place in the Eastern Conference, while Vancouver improved to 7-7-3 (24 points).
It was the first home loss of the season for the Union, who are 6-1-2 at home. It was Vancouver's first win at Talen Energy Stadium after being 0-1-2.
"I am [angry] about that," Union coach Jim Curtin said about the recent defensive slump. "Don't get me wrong, and we will get it fixed, but [we have given up] a lot of silly goals, I would say."
The Union began attacking immediately. Tranquillo Barnetta was stoned in front by sliding keeper David Ousted, who was making his 101st straight MLS start, in the fourth minute.
Union forward C.J. Sapong missed his third straight MLS game with a right ankle sprain. Fabian Herbers once again replaced him.
Herbers helped set up the first goal, when he fired a shot off the left post from just inside the box that bounced off Sebastien Le Toux to Roland Alberg, who continued his hot streak by scoring from seven yards out in the 14th minute.
Counting a U.S. Open Cup game, Alberg has scored in four consecutive matches with seven goals in that time, five in three MLS games.
Vancouver tied the score in the 19th minute off a miscue by keeper Andre Blake, who saw a corner kick slip through his hands to Andrew Jacobson. The former Union midfielder headed the ball in at the far post.
"There will be times you make mistakes. Unfortunately that mistake cost us a goal, but I can't dwell on it," Blake said.
Vancouver's Kekuta Manneh outran the Union defense from beyond midfield to break the tie. He split between Josh Yaro and Richie Marquez, firing a shot from the top of the box. The shot hit the left post and bounced into the net in the 41st minute for his fifth goal.
Curtin suggested that Yaro might have been better off taking a foul, but the rookie center back felt otherwise.
"I don't want to go down and maybe foul him because I thought I was the last guy," Yaro said.
Vancouver took a 3-1 lead in the 84th minute on a Christian Bolanos shot from just inside the box, which turned out to be necessary when Chris Pontius scored on a tip-in during stoppage time.