The postseason tipped off for the Liberty on Sunday at Barclays Center, beginning with a series that should, in theory, bring them the least amount of peril.

Sure, Atlanta beat them here Thursday night. But the Liberty had nothing to play for, already having clinched the top seed/best record/home-court advantage throughout the WNBA playoffs. The Dream needed that game to claim the eighth and final seed.

Still, the Liberty weren’t thrilled with how they played in that one — or the last few weeks, for that matter.

Coach Sandy Brondello made a major lineup change and the 20/20 focus was there for Game 1 of the best-of-three opening round. The Liberty hope it was the start of a run that will end with a celebration of the franchise’s first WNBA championship.

The Liberty shot out to an 18-point lead in the first quarter and rolled to an 83-69 win. They can clinch their ticket to the best-of-five semifinals against two-time defending champ Las Vegas or Seattle with a Game 2 win on Tuesday night at Barclays.

“If you lose a game here, you lose home court,” Brondello said. “ . . . We’ve got big goals. We worked hard to get the No. 1 seed. So we didn’t want to let it go down the drain.”

Brondello inserted a weapon that the Liberty didn’t have last year in their run to the Finals. Leonie Fiebich, named to the AP’s All-Rookie team on Sunday, started in her first WNBA playoff game after filling in as a starter 15 times during the regular season.

The 6-4 German guard, an MVP in Spain the past two seasons, replaced 35-year-old point guard Courtney Vandersloot, with Sabrina Ionescu able to do the primary ballhandling duty.

“It was going to help us with our best lineups at all times,” Brondello said. “ . . . [Vandersloot] can kind of run that second unit.”

Fiebich had her best scoring day in the WNBA, a Liberty-leading 21 points. She shot 7-for-8, including 4-for-4 from three-point range. She also brought her length on defense and made two steals.

“I started for this team already,” she said, “so I didn’t feel super-nervous because of that.”

Vandersloot had four points, three assists and two steals. The third assist gave her a WNBA career postseason record. It was assist No. 365, pushing the five-time All-Star past Sue Bird.

But it came in Vandersloot’s first reserve duty since 2017.

“It’s never a good feeling to go from the starting lineup to the bench,” she said. “But I’m true when I say that I want the best for the team. And I do think it was a smart, efficient change.”

Breanna Stewart contributed 20 points and 11 rebounds, and Ionescu delivered 17 points. Rhyne Howard topped the Dream with 14. “I think their physicality really bothered us,” Atlanta coach Tanisha Wright said.

The Liberty began the day by going 6-for-6 from the floor and 6-for-6 from the line. They didn’t miss a shot of any kind until 2:33 remained in the first quarter. That set a WNBA postseason record for the longest amount of game time elapsed from the start without a miss.

Fiebich nailed her first three-pointer to make it 13-4, and after the Dream scored the next five points, the Liberty took off on a 14-0 run. When Ionescu, who scored 12 in the quarter, nailed a three-pointer, the lead was 27-9.

By the end of one, it was 29-16. The Liberty shot 72.7% from the floor — a franchise postseason record for the first quarter — and held Atlanta to 35.3%.

By halftime, it was 48-30. Fiebich had 15 points and hadn’t missed a shot, going 5-for-5, including 3-for-3 on three-pointers.

Asked how do you say “on fire” in German, Fiebich said, “I don’t think we have that. In basketball, we use a lot of English words. So ‘on fire’ would work.”

The lead reached 22 in the third.

“We’re still a confident bunch,” Wright said. “We’re still positive. They punched us in the mouth. That’s exactly what they were supposed to do. They’re in their home . . . Now we have to learn how to respond to it.”