Another victory over its regional rivals will vault it into first place in the Western Conference.
RSL looks to extend its eight-game unbeaten streak in the series Saturday night against host Colorado, which will try to end its franchise-record six-game losing skid.
Salt Lake (13-7-3) has won three of its last four MLS matches, most recently beating Vancouver 2-1 on July 27 as Alvaro Saborio scored both goals.
Saborio scored and added an assist in a 2-0 victory over Colorado on July 21 to clinch another Rocky Mountain Cup, awarded to the club that wins the season series.
RSL, which also beat the Rapids 2-0 on April 7 with the help of another goal from Saborio, is 4-0-4 in its last eight meetings with Colorado and hasn't lost to the Rapids since May 2, 2009.
Salt Lake, though, fell 1-0 at Costa Rican club Herediano in a CONCACAF Champions League match Tuesday, and key defender Jamison Olave went down with a hamstring injury.
"He's really an honest player. He wants to learn our system," Borchers said of Watson-Siriboe. "He's really athletic, he's good on the ball, he's got a lot of potential and we're just giving him confidence."
Salt Lake, which trails idle San Jose by two points in the West, should have plenty of confidence heading into its match with the struggling Rapids (7-14-1), who have dropped eight of their last nine after falling 2-1 to Seattle last Saturday.
Colorado started 4-1-1 at home but has dropped four of five since, including three straight. Coach Oscar Pareja can't seem to pinpoint the problem, as the Rapids haven't been able to take advantage of visiting teams playing in the high altitude.
They haven't lost four straight home matches since May 19-June 16, 2001.
"To give you an accurate answer at this point is difficult," Pareja told the team's official website. "We have to be better, especially at home, especially with the altitude, with all those things. Period."
Colorado, which has been outscored 11-4 during its overall slide and has allowed two goals in each of the last five matches, still hopes to make a run at the postseason.
"I think we still got a good thing here and there's a lot of points on the board still," goalkeeper Matt Pickens said. "We need to make sure we try to get as many as we can out of the next 12 games to get into the playoffs."
Salt Lake has been outscored 7-0 while dropping its last two MLS road matches.
- Colorado Rapids
- Alvaro Saborio