Meanwhile, Atlanta got one of the best individual performances in playoff history from Angel McCoughtry in the first round. On Sunday, the Dream head to Chicago, where they hope to avenge a painful playoff series loss to the Sky two years ago.
Awaiting the winners are No. 1 seed Minnesota and No. 2 Los Angeles.
No. 8 Phoenix vs. No. 3 New York (NBA TV, ESPN3, 7 p.m. ET Saturday)
Here's the deal with the Mercury: No one would have been stunned to see them lose in the first round at Indiana. But no one will be stunned to see them move on to the semifinals. That's how hard it has been to predict what Phoenix might do.
It has been an up-and-down season for the Mercury because they couldn't count on their defense, which is the very thing that was a rock for them when they won the WNBA championship in 2014.
During the 2016 regular season, Phoenix allowed foes an average of 83.3 points per game. The Mercury's effort in their 89-78 victory over the Fever on Wednesday was much closer to what they'll need to beat the Liberty. The Mercury held the Fever to 37.2 percent shooting while shooting 54.5 percent themselves.
"Any night we play good team defense, we pack the paint around the ball and get on shooters, the results come out in our favor," Phoenix's Brittney Griner said. "We know what we need to do now; everybody has to go up another level."
Phoenix got important offensive contributions from several players on Wednesday, with Diana Taurasi leading the way with 20 points. Griner and DeWanna Bonner each had 18, and Candice Dupree and Penny Taylor each scored 12.
Bonner has been coming off the bench the past five games, with Marta Xargay starting instead, and that worked well for the Mercury on Wednesday. Bonner was fresh and very effective in the fourth quarter, scoring 11 of her points to hold off the Fever.
It was an emotional night, as Indiana's Tamika Catchings played her last game, but it could also have been the last for Australia's Taylor. Now Saturday's game will be the end for either Taylor or New York's Swin Cash, who is also retiring at season's end.
Neither the Mercury nor the Liberty played much defense in their first meeting this season, a 104-97 Phoenix victory in New York on June 26. Dupree had a season-high 26 points in that game, going 11-of-13 from the field. Tina Charles had 26 for New York but took 27 shots to do it. And the Liberty went 12-of-15 from the line compared with the Mercury's 27-of-33.
The second meeting, in Phoenix on July 1, was more the type of game that defined the Mercury much of the season: They scored a lot, but they gave up a lot more. New York won 99-88, led by Charles' 31. This time, the Liberty were able to match -- actually, slightly exceed -- the Mercury going to the line, with New York at 25-of-29 and Phoenix 23-of-26.
The last game, though, was a Liberty blowout: 92-70 on Sept. 3 in New York. Phoenix shot just 32.8 percent from the field, and Griner had her lowest output of the season with two points. The Liberty held Griner's offense down without center Kiah Stokes, a defensive specialist who has been out since Aug. 26.
"We're a bit of a toss-up," Taurasi said of the Mercury this season. "But since the Olympic break, we kind of know who we are. Everyone is healthy. We see ourselves playing differently and feeling differently."
Even so, Phoenix was 6-4 after the Rio Games going into the postseason, so "toss-up" really is probably the best way to put it. However, as they showed at Indiana, the Mercury are especially hard to beat when they face elimination. That's the Taurasi factor as much as anything. New York will have to find a way to limit her, which Indiana could not do.
No. 6 Atlanta at No. 4 Chicago (ESPN2, 1 p.m. ET Sunday)
Wednesday, the Dream didn't have their second-leading scorer, Tiffany Hayes, who was out because of a suspension after her seventh technical foul in the regular-season finale. They didn't have inside veteran presence Sancho Lyttle, who is injured.
But they had McCoughtry, who knew she had to put the Dream on her back. She did just that in a 94-85 victory over Seattle, scoring 37 points to go with seven assists and three rebounds. She shot 66.7 percent from the field (14-of-21), which also was critical. During the regular season, she shot 43.4 percent.
It was one of McCoughtry's finest performances, and it couldn't have come at a better time. But rookie Bria Holmes also had a very timely big game, playing all 40 minutes and finishing with a season-high 21 points, plus seven rebounds and three assists.
Seattle No. 1 pick Breanna Stewart, who's sure to win rookie of the year, had 19 points, seven rebounds and three assists. But her first WNBA season came to a close, while Holmes, who was drafted No. 11 out of West Virginia, moves on.
The Dream prevailed 2-1 in the regular-season series with the Sky, winning the first two games in Atlanta, 87-81 on May 22 and 101-97 on June 17. In the teams' first game back after the Olympics, the Sky won 90-82 in Chicago on Aug. 26.
The big difference is that Elena Delle Donne, last season's MVP, had 34 points in that victory over Atlanta, but now she's out after thumb surgery. And although the Sky actually played surprisingly well in five games without her -- winning three, including against Minnesota -- there's no getting around the big void it leaves for Chicago.
Defense is going to be key for the Sky, which is a worrisome proposition. That hasn't been the Sky's strength, not this season or in recent ones. And no team is more successful getting to the line than the Dream, who went there a league-high 909 times in the regular season. However, they made just 75.1 percent (683); only Connecticut was worse at the stripe (71.5.) So against the Sky, the Dream not only have to draw fouls, they also must convert the free throws.
Few are better at that skill than Delle Donne, who shot 93.5 percent from the line this year and is at 93.8 percent for her career. But with her out, the Sky have been led by veteran Cappie Pondexter, who averaged 22.3 points in four games after Delle Donne's injury. Neither Pondexter nor Courtney Vandersloot played in the Sky's regular-season finale at Seattle, as that had no impact on their seeding.
In 2014, the Dream and the Sky met in the Eastern Conference semifinals (in the WNBA's old playoff format), with Atlanta as the No. 1 seed and presumed favorite. But Chicago won the series 2-1, rallying from 16 down after three quarters in Game 3 in Atlanta. Delle Donne had 34 points in that 81-80 victory, and the Sky then went on to beat Indiana in the East finals before losing to Phoenix in the WNBA Finals.
That tough defeat at home to end 2014 sat irritatingly with Atlanta through last year, as the Dream didn't make the playoffs. Now they hope to end the Sky's season at home this year.