Philadelphia is already in trouble in its Eastern Conference semifinal series against Toronto, and 76ers coach Brett Brown might be one of the biggest reasons why.

It’s not that Brown made coaching mistakes in Game 1.

Instead, he might have not made enough mistakes in 2012 and 2013.

Let’s explain: Kawhi Leonard’s first two years in San Antonio were Brown’s last two years as an assistant for the Spurs. When Brown left Gregg Popovich’s staff to take over as coach of the 76ers after the 2012-13 season, he was well aware that Leonard was on the path to becoming something special. And now, after seeing Leonard put up 45 points in Game 1 of this 76ers-Raptors series — a 108-95 win by Toronto — it’s up to Brown to figure out how to slow that superstar when the series resumes with Game 2 on the Raptors’ home floor Monday night.

“Every year, he gets more dominant,” Brown said. “Even when I came to Philadelphia, those years that I was in Philadelphia looking in the rear-view mirror of him evolving under Pop and in the San Antonio Spurs’ system, you could just see this thing’s trending in an incredible way.”

Brown was considered a player-development master during his long tenure the Spurs. Watching the way Leonard control play in Game 1 on Saturday night — 45 points and 11 rebounds on 16 for 23 shooting — perhaps he regretted whatever role he played in the 2014 NBA Finals MVP’s formative pro years.

With Leonard on the floor, Toronto outscored Philadelphia 97-71.

With Leonard on the bench, Toronto was outscored 24-11. He sat for three stints, and Philadelphia cut into Toronto’s lead every time.

“This is going to be erased,” Leonard said, dismissing any notion that the Raptors’ success on Saturday would carry over to Monday night. “Starting back from scratch, 0-0. And we’re going to have to try to come out to win Game 2.”

Game 2 of the Toronto-Philadelphia series is one of two games on Monday’s schedule. The other is a Western Conference semifinal series opener, with third-seeded Portland going to second-seeded Denver.

There’s much more for the 76ers to be fretting over than just Leonard.

Even with point guard Ben Simmons shooting 7 for 8, Philadelphia’s starting five shot 41 percent. 76ers star Joel Embiid struggled against Toronto’s defensive scheme, one led by former defensive player of the year Marc Gasol; Embiid has never scored more than 16 points when facing him. JJ Redick led Philadelphia with 17 points in Game 1; Leonard and fellow starting forward Pascal Siakam both had 17 points for Toronto by the end of the first quarter.

“We clearly need to be better offensively,” Redick said. “And then on the other side of the ball, I don’t think we executed our game plan particularly well.”

NO UPSETS

For the first time since 2008, there were no upsets in the first round. The top four seeds advanced out of both the East and the West, something that also happened in 2004, 2002 and 1997. Odds say there will be at least one mild upset soon; the last time the higher-seeded teams won every matchup through the first two rounds of the playoffs was 1986.

MONDAY’S GAME: 76ERS AT RAPTORS

Raptors lead 1-0. Game 2, 8 p.m. EDT, TNT

NEED TO KNOW

Leonard and Pascal shot a combined 28 for 38 for 74 points in Game 1, outscoring Philadelphia’s starters by themselves. The Raptors have never blown a 2-0 series lead (in fairness, they’ve been in that situation only once) and the 76ers have never won a series where they lost the first two games (that has happened 18 times).

INJURY WATCH

Key reserve Mike Scott (right heel) was clearly missed by Philadelphia in Game 1. His status for Game 2 is questionable.

KEEP AN EYE ON

Philadelphia’s defensive adjustments. Siakam and Leonard combined to take 19 of Toronto’s first 23 shots in Game 1 (and they were 15 for 19 in that stretch). Expect the 76ers to try anything and everything to keep them from getting on another early roll in Game 2.

PRESSURE IS ON

Embiid and Jimmy Butler. Philadelphia’s two highest-paid players struggled mightily in Game 1. Embiid was 5 for 18 from the floor, 4 for 12 from inside the lane. Butler shot 3 for 5 around the rim and 1 for 7 everywhere else.