Mohegan — The Las Vegas Aces weren’t at Mohegan Sun Arena on Tuesday to celebrate last season’s WNBA championship, which came on that same floor.

Instead, Aces head coach Becky Hammon referred to the game with the Connecticut Sun, a rematch of last year’s league finals, as a business trip.

It was almost businesslike, too.

The Aces triumphed 90-84 but not before a second-half 3-point barrage by Connecticut’s Bec Allen carved the Las Vegas lead from 19 to 3 with 3 minutes, 50 seconds remaining, sending the 4,368 fans at Mohegan Sun and her teammates into a frenzy.

Allen, who came off the bench to lead the Sun with 22 points, was 6-for-7 from 3-point range, as the Sun pulled to within 76-73 after No. 6.

“Certainly disappointed that we didn’t come out with a win, disappointed with the way that we started the game,” said Sun head coach Stephanie White, whose team trailed 48-31 at halftime with 12 turnovers.

“But proud of our effort in the second half that we regrouped, that we kept coming at them. Nobody wants to come out without winning a ballgame but we’ve got some good momentum that we can build on.”

The Sun (6-2) and the Aces (7-0) topped their respective conference standings entering the game. They will meet again at 7 p.m. Thursday at Mohegan Sun in Game 2 of the regular-season series.

Las Vegas defeated the Sun 3-1 in last year’s WNBA Finals, with the Aces taking Game 4 78-71 and earning the right to celebrate on the Sun’s home floor.

On Tuesday, A’ja Wilson led the Aces with 23 points, 10 rebounds and four blocked shots. Jackie Young had 22 points, seven rebounds, six assists and three steals and Kelsey Plum added 17 points and five assists.

In addition to Allen, Brionna Jones had 15 points and 10 rebounds for the Sun and Alyssa Thomas had 14 points, 11 rebounds and five assists for her seventh double-double in eight games. DiJonai Carrington and Natisha Hiedeman finished with 11 points each.

The Sun outscored the Aces 31-20 in the fourth quarter.

“That’s a championship-caliber team,” Hammon said, asked of the Sun’s fourth quarter. “They’re not going anywhere. They’re not going to miss every shot.

“The good thing is that we played solid enough and we buckled down enough toward the end of that fourth quarter to walk out of here with the win. But we never like it when one person (Allen) makes more 3s than our entire team.”

The Aces took the commanding 17-point lead at halftime with the Sun struggling offensively, shooting just 31.2%. Las Vegas pushed the lead to as many as 19 on a layup by Plum that made it 48-29 before the Sun’s Hiedeman closed the scoring in the half with two free throws.

Young had 11 points in the first half for the Aces and Plum and Chelsea Gray had 10 each. Thomas had eight points and five rebounds in the opening half for the Sun.

Las Vegas still led 70-53 after three quarters, but Allen, who hit two 3-pointers in the third, soon started firing in quick succession as the fourth began.

A basket from Jones, assisted by Allen, started a 12-0 Sun run. Allen hit her fifth 3 to pull within 76-66 and Carrington scored four consecutive points before Allen’s sixth strike made it a three-point margin at 76-73.

Following a timeout, however, the Aces got a basket from Wilson and a 3 from Plum to push the lead back to eight. Young’s three-point play with 1:15 to play made it 84-77 in the Aces’ favor. Hiedeman’s 3 carved the Vegas lead to four one more time at 86-82.

The six 3s tied a career high for Allen, the 6-foot-2 Australian guard who is in her first season with the Sun after being traded in the offseason as part of a deal which sent all-star Jonquel Jones to the New York Liberty.

“I mean, when I first found out that Bec was coming to our team, I was super excited ’cause she’s a knockdown shooter,” the Sun’s Jones said. “I know that every time it’s going up, it’s going in. Today she showed what she brings to the team.”

Said White: “Between now and Thursday, we’ve got to fine tune, we’ve got to rest, we’ve got to recover. The great thing is we’re not preparing for a new opponent. We have to really be locked into adjustments we want to make, we have to be disciplined in terms of our recovery and be ready to go on Thursday.”

v.fulkerson@theday.com