With Zac MacMath deputizing in goal, Colorado took the lead in the 29th minute when Kevin Doyle raced into the box to head home Marlon Hairston's cross.
MacMath held RSL at bay, but the game turned after a free kick in the 85th minute. Luis Silva headed the ball onto the crossbar and it came back to Chris Wingert, whose shot was blocked by the arm of Colorado's Jared Watts. The defender was sent off and Yura Movsisyan converted the resulting penalty.
And three minutes later RSL made the extra man count as Lennon -- a 19-year-old U.S. youth international on loan from Liverpool -- made a mazy run through the Rapids defense before unleashing a low shot from 25 yards out past MacMath to win it.
Cyle Larin volleyed home a winning goal in the 91st minute to help Orlando City beat the LA Galaxy 2-1.
Will Johnson fired in a bouncing ball to give Orlando a ninth-minute lead, which held up untilRomain Alessandrini's equalizer in the 83rd minute.
Alessandrini controlled the ball atop the box, turned a defender and fired in a low shot for his fourth goal in the past three games.
But Larin, who also moved his tally to four goals, got free in the box to turn in Will Johnson's corner in stoppage time for Orlando, which is second in the Eastern Conference after a fourth win from five matches.
The Galaxy slumped to a fourth defeat from their opening six games.
Anthony Jackson-Hamel scored deep into stoppage time to give the Montreal Impact their first win of the season, 2-1 over Atlanta United.
Kenwyne Jones gave Atlanta the lead with his first MLS goal after the visitors took advantage of a poor kick from Montreal keeper Evan Bush.
But Atlanta then had center-back Leandro Gonzalez Pirez sent off just before half-time in a controversial penalty decision for a foul on Matteo Mancosu, and Ignacio Piatti equalized from the spot.
And the man disadvantage proved too much as Montreal found the winner in the 93rd minute,Jackson-Hamel redirecting a long shot from Hernan Bernardello inside the post.
Nemanja Nikolic scored twice, Bastian Schweinsteiger added a goal and the Chicago Fire beat the New England Revolution 3-0.
New England, which had a three-game unbeaten streak snapped, played most of the match a man down after Je-Vaughn Watson was sent off in the 27th minute after receiving a pair of yellow cards just minutes apart.
Taking advantage of the man advantage, Schewinsteiger split a pair of defenders and, from just beyond the top-left corner of the six-yard box, side-footed a low finish for Chicago to open the scoring moments before halftime.
Nikolic made it 2-0 early in the second half, poking Luis Solignac's deflected entry past Cody Cropper from point-blank range, then capped the scoring in the 73rd minute.
Schweinsteiger fed David Accam, streaking down the left sideline, who placed perfectly a cross to the spot where Nikolic tapped it into the net.
Dom Dwyer scored in the 53rd minute and undefeated Sporting Kansas City won its first game on the road this season, a 1-0 victory at the Portland Timbers.
Sporting KC remained one of just two teams in MLS without a defeat. Sporting's stout defense, which has allowed only two goals through six games, slowed a Portland side that leads the league with 16 total goals.
Dwyer broke through with his first goal of the season, scoring with a header in the 53rd minute following a cross from Jimmy Medranda, fending off Portland's Marco Farfan.
Portland turned up the pressure in the final 15 minutes. Darron Mattocks tried unsuccessfully to chip a shot past Sporting goalkeeper Tim Melia, who really came up big moments later when he tipped Darlington Nagbe's hard shot from distance, which caromed off the crossbar.
Ola Kamara and Justin Meram scored as Columbus Crew SC erased an early deficit to beat Toronto FC 2-1.
The visitors had gone ahead through Jozy Altidore's goal, the U.S. striker heading home Victor Vazquez's corner kick in the 21st minute. Toronto then nearly doubled its lead butZack Steffen pushed Sebastian Giovinco's shot around the post.
But it was all Columbus from there asKamara stayed onside to tap the ball into an open net in the 37th minute, and Meram added a second six minutes later by flicking the ball into the net after a corner kick.
Alex Muyl and Bradley Wright-Phillips scored as the New York Red Bulls beat D.C. United 2-0 to end a four-game winless streak.
Muyl opened the scoring just seconds into the second half, heading home a corner kick by Sacha Kljestan from the top of the 6-yard box. It was the first goal of the season for the 21-year-old homegrown player and the third of his MLS career.
Wright-Phillips perfectly timed his run, took a pass from Felipe Martins near the right corner of the six-yard box and fired it through the legs of Bill Hamid into the net in the 62nd minute.
Luis Robles, who led MLS last season with 11 clean sheets, had three saves -- including a diving stop on Lamar Neagle's shot with four minutes to play. The Red Bulls are unbeaten in their last 17 regular-season matches at home, including 11 shutouts.
Minnesota United fought back from a two-goal halftime deficit to secure a 2-2 draw at the Houston Dynamo.
Houston took the lead in the 14th minute when Erick "Cubo" Torres found Mauro Manotas, who had time to take a touch in the box before spinning and shooting, and Alberth Elis doubled the lead following a set piece two minutes before halftime.
But Christian Ramirez got a goal back for Minnesota two minutes after the break with a header following a corner, and the comeback was complete as the ball fell in the box for Johan Venegas to equalize in the 59th minute.
Colorado 1-2 Real Salt Lake: RSL leave it late
Real Salt Lake scored two late goals to overcome Colorado and win the first Rockey Mountain Cup match of the year.
Orlando City 2-1 LA Galaxy: Larin leads Lions - Via MLS
Cyle Larin's volley in stoppage time lifted Orlando City past LA Galaxy for their fourth-straight win at their new stadium.
Montreal 2-1 Atlanta: Impact win it late - Via MLS
Montreal Impact beat Atlanta United for their first win of the season via a late, deflected goal by Anthony Jackson-Hamel.
Chicago 3-0 New England: Fire rout Revs - Via MLS
Nemanja Nikolic and Bastian Schweinsteiger bagged the goals as Chicago easily handled 10-man New England.
Portland 0-1 Sporting KC: Dwyer lifts SKC
Dom Dwyer and Tim Melia were the heroes for Sporting Kansas City as they earned a big away win at Portland.
Columbus 2-1 Toronto FC: Crew storm back
Toronto led early through an early Altidore header, only for the home side to score two in the first-half to claim the win.
NYRB 2-0 D.C. United: BWP on the mark - Via MLS
Bradley Wright-Philips and the Red Bulls were able to stifle D.C. and turn on their trademark style in their 2-0 win.