Now his younger brother is temporarily keeping his seat warm at the Rogers Centre, while Pompey wraps up the Blue Jays' final road trip of the season.
Tristan is among 160 of Canada's top draft-eligible players competing in Tournament 12, a five-day amateur baseball showcase at Toronto's home stadium, which comes to a conclusion Saturday. Getting to play on the same field as his 21-year-old brother has Pompey dreaming big.
"I could be here, too, some day, that's what it tells me," he said. "It's super surreal that they give us guys the Major League field. It means a lot. It means I have worked hard and I deserve to be here amongst all these great players.
"It's pretty sweet knowing that Dalton's in the same position that I am in in the outfield, and he's shagging balls out there and I'm doing the same thing."
The Pompey brothers look the same. Both play the outfield and have shared the same goal of becoming big leaguers since they were kids.
Both played basketball growing up, too, but their mother Valerie Pompey said baseball was always the No. 1 passion of her only kids.
"Right from the beginning they were just good at it," she said, while watching her youngest participate in a tournament game.
It's clear they made the right choice to give up the hardwood for the diamond.
Dalton started the 2014 season at Class A Advanced Dunedin and advanced to the Majors, while Tristan continues to make his own strides as a player.
A scout for a Major League club in attendance at Tournament 12 singled out Tristan as one of the key Canadian position players leading up to the 2015 First-Year Player Draft. The 17-year-old, who has a lean build like his brother, said his speed and contact rate are two areas of his game which have improved most.
Pompey, clocked with one of the fastest 60-yard times during a pre-tournament workout, has gone through extensive lower- and upper-body exercises to become more explosive and agile.
The 6-foot-3, 180-pounder has also received guidance from former Expos great and current Blue Jays baserunning coordinator Tim Raines.
Dalton enjoyed similar improvements this season in the running and hitting departments, evidenced by his career-high .317 average and 43 stolen bases across three Minor League levels.
The similarities they share come from having a strong brotherly bond.
"We are really close," Tristan said. "We are four-and-a-half years apart but it's almost like we are twins -- we are that close together."
Dalton is an alumnus of Greg Hamilton's Canadian Junior National Team, and Tristan could soon join the prestigious program if he continues on the right development path. Hamilton, the director of Baseball Canada's national teams, recognizes the similarities between the two but doesn't believe they are a carbon copy of one another, either.
"I think Tristan is going to be a little different -- they aren't going to be the same player," Hamilton said. "Tristan certainly has the prerequisites to be a really good player; it might not turn out to be the same form of player as Dalton.
"But he has some gifts. He's an interesting player who certainly has a chance to be a really good player."
Valerie and her husband, Ken, have always had confidence in their boys, but even they were caught by surprise when their eldest got the call to the big leagues.
"We thought it was going to happen one day, just not that fast," Valerie said.
She was out watering the plants when the phone rang, a call she didn't reach in time. It was Dalton Pompey and, moments later, as she tried calling him back, he sent a text saying "Mom, I'm going to the big leagues."
"I was so flustered I couldn't even dial his number," Valerie said. "I was so excited, I couldn't believe it."
As Pompey told the story of her kids' baseball journeys and snapped photos of her youngest son participating at Tournament 12 on the same field her oldest now calls home, she felt a wave of nostalgia.
"When I see Tristan out there it brings tears to my eyes because I think about my older one," she said.
Tears of joy, of course. Something she hopes there will be more of in the future.