Salt Lake (3-1-3, 12 points) snapped a three-game winless streak with two goals in injury time to earn its second home victory of the season.
Brian White scored a second-half goal on his Whitecaps debut, but it wasn't enough to keep Vancouver (2-5-1, 7 points) from taking its fourth loss in a row.
Erik Holt made it 2-1 two minutes into second-half stoppage time when he headed home a pass from Aaron Herrera. Kreilach added his second goal three minutes later with a header from a cross from Justin Meram.
Aggressiveness paid off for Salt Lake with Kreilach's opening goal in the 43rd minute. Albert Rusniak back-heeled the ball to him outside the top of the box. Kreilach teed up and blasted the ball down the middle to put RSL ahead.
Vancouver levelled with White's 16th career MLS goal in the 54th minute. Javain Brown sent a cross down to the back post and White tapped in a left footer, threading the ball just inside the post for the equalizer before Salt Lake's late show sealed the win.