As a junior in high school, Justen Glad was faced with an irrevocable and life-changing decision: would he play college ball at Stanford or sign with Real Salt Lake?

“What it came down to pretty much was just losing time,” said Glad of his decision to go pro at 17, “and having a dream and wanting to pursue it and pursue it full-fledged, as opposed to maybe wait a year and a half and then see what happens.”

After training Thursday, Glad second-guessed himself while trying to remember how many seasons ago he had become a regular starter for RSL. Even he could hardly believe it has already been two years. Barely at a legal drinking age, Glad signed his first MLS contract four years ago. He received his first call-up to U.S. senior national team camp in January. And somehow, despite his youth, over the past three matches Glad has found himself thrust into the position of the most experienced player on the back line.

Injuries wiped out the presumed starters — and in some cases their backups — on either side of him. To Glad’s right are Nick Besler, who made his MLS debut last month, and Brooks Lennon, a winger-turned right back. To his left is Pablo Ruiz, a 19-year-old central midfielder converted to left back.

“As with any partnership, it’ll definitely take time,” Besler said of his union with Glad, “but I think we do a good job of balancing each other out.”

Glad is familiar with the situation the other defenders are in, getting a chance because of injuries.

Real Salt Lake at Philadelphia Union

At Talen Energy Stadium, Chester, Pennsylvania

Kickoff » 5:30 p.m.

TV » KMYU, Univison

Radio » 700 AM

Records » RSL 4-5-1, PHI 3-5-2

Last meeting » RSL 1, PHI 0 (May 27 at Rio Tinto Stadium)

About Philadelphia » Has never beaten RSL, with a 0-4-6 all-time record against the Salt Lake side. … Goalkeeper Andre Blake is coming off his 20th shutout, which he claimed at Montreal last weekend. ... Corey Burke is suspended due to red card received last week. … Richie Marquez (sports hernia surgery) and Josh Yaro (concussion) are sidelined for the match due to injury.

About RSL » Winless on the road so far this season (0-4-1). ... Goalkeeper Nick Rimando is undefeated against Philadelphia since joining RSL. … RSL defenders Tony Beltran (knee), Shawn Barry (knee), and Demar Phillips (ankle) are listed as out for the match. … Goalkeeper Alex Horwath (achilles) and midfielder Jordan Allen remain sidelined due to injury. … Forward Joao Plata (quad) are questionable for the match.

Glad made his MLS debut in May of 2015, in place of an injured Tony Beltran. Beltran had traveled to Vancouver, Glad remembers, so he didn’t find out he was starting until the day before the match.

“There’s always that little bit of excitement at the very beginning,” Glad recounted, “and then as soon as the game starts, the whistle blows, it’s kind of game mode, and you forget about everything around you and the fact that you’re in a stadium. You’re just focused on what’s going on in the field.”

Then-coach Jeff Cassar sang Glad’s praises after the 2-1 loss, and slid him back into the starting lineup twice in just the next month. The following season Glad started 27 matches.

Now an established player, Glad began this season in a slump. He made uncharacteristic errors in his positioning and passing. But the last two matches, those mistakes, while still present, haven’t been quite as ghastly.

“The normal fan might not notice some of the things [I’m working on],” Glad said, “but when I go back, when I look at video there’s things that I look at in terms of, if I should be a couple steps over to the right if that ball’s out wide … and just little improvements like that.”

He remains engaged in training even when he doesn’t have to be, eyes trained on the ball, shifting from side to side while he’s on a perimeter of a drill.

“All players go through dips and valleys,” RSL coach Mike Petke said. “...But Justen’s a smart, motivated young kid, and I know Justen’s going to be fine.”

While his recent play on the field hasn’t met the standard he set for himself, Glad said he has developed leadership skills over past couple years. RSL has needed his positivity through a slow start to the season, and on an inexperienced back line.

Veteran center back Marcelo Silva could be back in the starting lineup alongside Glad Saturday at Philadelphia. Silva, recovering from a groin injury, has been training in full and played 45 minutes with RSL’s USL affiliate, the Real Monarchs, on May 4.