Maya Moore scored 20 points to power the Lynx to a 75-67 victory Thursday night, snapping the Mercury's franchise-record 16-game win streak.
Seimone Augustus added 19 points for Minnesota (21-6), which won its eighth straight.
''We kept believing, stayed with it, kept sharing the ball,'' Moore said after the Lynx shot just 38 percent but frustrated the Mercury with defense. ''Nobody was trying to individually do it on their own.''
The teams have clinched the top two spots in the West and home-court advantage in the first round. Phoenix, which won the first two matchups, had its lead for the top seed cut to 1 1/2 games.
Brittney Griner scored 18 points for the Mercury (22-4), who lost for the first time since June 12. Phoenix's streak was the second-longest in WNBA history, trailing only Los Angeles' 18-game run in 2001.
Phoenix came in leading the league at nearly 50 percent shooting from the field, but was just 37 percent (25 for 68) against the Lynx - led by Diana Taurasi's 5-for-21 effort.
''You won't see Diana shoot like that very often, but she also got a lot of attention,'' Mercury coach Sandy Brondello said. ''Could she have gotten a few more calls? Yes, definitely. Maybe we'll get them next time. But she's a competitor. She'll bounce back.''
Taurasi finished with 10 points, going 0-of-7 on 3-point attempts, and was whistled for five fouls, including a technical. She offered some sarcastic commentary on the physical nature of the game.
''We've got to get better at football. We will,'' she said. ''If we have to put our helmets on, that's what we're going to have to do from here on out. Like I said, we'll be ready to play football next time.''
After missing their first seven shots, Minnesota used an 11-0 run to take a 21-10 lead into the second quarter. It was quite a change for the Mercury, who have been burying teams early over the course of their record hot streak.
''I remember thinking that we were very fortunate, because if our defense wasn't as good as it was, and we're not making shots, we've got a problem,'' Minnesota coach Cheryl Reeve said. ''Every time you play Phoenix, the first quarter is really important. These guys have had double-figure leads in the first half almost every time they've played in this streak. So we were really locked in.''
By halftime, Phoenix had cut the Lynx lead to 39-36 thanks to 12 points from Griner and 11 from Penny Taylor, who finished with 16. Lindsay Whalen scored Minnesota's last six points of the first half, leading the team with nine at the break.
The Lynx led 52-51 at the start of the fourth quarter, but found some breathing room near the seven-minute mark when Moore hit back-to-back 3s to open up a 12-point advantage.
Taurasi's jumper with 1:28 to play pulled the Mercury to 69-65, but they would get no closer.
The Lynx visit the Mercury on Aug. 9 in the teams' final regular-season meeting.