Liberty fans have waited 27 seasons for a W.N.B.A. title, and on Friday night, it showed. The atmosphere at Barclays Center was electric for New York’s opening postseason game against the Washington Mystics.

Fans waved white playoff towels, booed every call that didn’t go their way and cheered for each celebrity featured on the scoreboard, including Malala Yousafzai, a Nobel Peace Prize winner; the tennis great Billie Jean King; and Teresa Weatherspoon, the former Liberty star. Members of the team’s N.B.A. counterparts, the Brooklyn Nets, were also in attendance.

Those fans were rewarded with a Liberty win, 90-75, behind 29 points from Sabrina Ionescu and 20 from Jonquel Jones. The game started as a tense back-and-forth affair, but the Liberty took a narrow lead into halftime, and they never relinquished it. Ionescu set a postseason franchise record with seven 3-pointers in the game.

After the Liberty wrapped up the regular season with a 32-8 record, expectations were high that they could take the championship. They are seeded second in the playoffs, with the Las Vegas Aces seeded first.

A win on Tuesday in Brooklyn, in Game 2 of this best-of-three series against the Mystics, would send the Liberty to the semifinals — and get them one step closer to that elusive title.