The Liberty were held to 63 points on 33.8% shooting, both season lows, as coach Sandy Brondello called her team's performance the worst of the season. Connecticut head coach Stephanie White, meanwhile, called the game "probably the most consistent 40 minutes that we've played all year."
Despite trailing by three at the half, the Sun won by 15, making them the seventh WNBA team -- and first since the 2011 Lynx -- to win a playoff game by at least that many after being down at halftime.
"We'll be better next time. I'm 100% sure of that," Brondello said. "That was their worst game of the season, but we've got great players and we will have to respond in the right way. It's a great challenge for us."
The Sun went 0-4 against the Liberty in the regular season but took control of the game early with a 25-21 first-quarter lead and used a 28-15 third frame to snatch the momentum. The loss was a first for the Liberty this postseason.
Both franchises are looking for their first championship, with the Sun making their fifth consecutive semifinal appearance and the Liberty making their first semifinal since 2015.
The Liberty made only 8 of 27 3s and were also outscored in the paint 34-22, with just four of those points coming in the second half. Their 14 turnovers led to 13 points on the other end, and they didn't get out in transition like they normally do, finishing with zero fast-break points for the first time this season. Connecticut also got its guards involved in crashing the glass, helping them win the rebound battle 35-30.
"They were being aggressive, blowing things up for us, but I don't think we handled it well," said two-time Finals MVP Breanna Stewart. "We didn't stay poised or composed. We had the ability to get to the second and third side, and we just didn't do that today. So it's a little bit frustrating to drop this one at home, but we'll bounce back."
Added 2021 MVP Jonquel Jones, whom along with Stewart and Courtney Vandersloot joined the Liberty this winter in what was the biggest offseason acquisition of collective talent the league has seen: "I felt like we just never got into New York-style basketball, being able to get stops and pushing the pace and stuff like that. It's always frustrating when you go back into a game when you feel like you didn't really put your best foot forward."
The Sun have been a strong defensive team all season, describing that as their identity even with a new head coach in White. But up until Sunday, they had failed to hold the Liberty to fewer than 80 points in a meeting this summer. Connecticut sought to finish plays and stay disciplined on that end of the floor and it largely succeeded in those endeavors.
The Sun crowded Stewart, who with Alyssa Thomas as her primary defender went scoreless from 3 (0 for 8) and went 7 for 25 from the field; limited the effectiveness of Jones (8 shot attempts); didn't let Sabrina Ionescu go off (12 points); and kept Betnijah Laney from finding a rhythm (3 points).
The Liberty viewed themselves as stagnant, indecisive and lacking energy at times, playing right into Connecticut's hands.
"They're such an offensive juggernaut that we just had to make things as difficult as possible, and I felt like our team really took ownership of that today," White said. "We were really proactive, our communication was at a high level, and when we had our lulls, we responded."
While Thomas and DeWanna Bonner get most of the shine from Connecticut, it was the Sun guards and wings who stepped up offensively: Natisha Hiedeman and Tiffany Hayes chipped in 12 points apiece, while Rebecca Allen came through with a playoff career-high 18 points off 4-for-6 shooting from 3.
Bonner added 15 points after halftime, which she said was because her fiancée, Thomas, "made me mad, and when that happens, I gotta show her a little something."
The Liberty will look to even the best-of-5 series with a Game 2 win at 8 p.m. ET on Tuesday.
"My messaging is 'OK, we just lost at home, we can't lose two at home. I mean, that's it,'" Brondello said of what she told her team after the game. "'That's what it comes down to. We've got to win this next game. This is our knockout game. And we've got to bring energy, whatever we need to do, we've got to make sure that we stay together most importantly. "We've lost the game, but we can make changes and we've got to all stay together and believe that we can get this done.'"