Montgomery made two free throws with 14.4 seconds left to help the Sun beat the short-handed Seattle Storm 60-58 on Sunday night.
"It was ugly, but we'll take it," Sun coach Mike Thibault said.
Tina Charles agreed with her coach.
"It was one of the ugliest games I've ever played in in my life," Charles said. "The turnovers they had (25), the turnovers we had (12). It was really frustrating, especially when you're a No. 1 team and you're going into the playoffs. You don't want to have these lapses going into the playoffs. Everything needs to be smooth sailing."
Connecticut shot 33.3 percent (23 of 69) from the field, including 2 of 14 from 3-point range.
Montgomery drew a foul against Camille Little to set up the free throws that made it 59-58.
"A little bit of skill, a little bit of luck and a little bit of bad defense on their part leaving their feet," Thibault said about Montgomery's pump fake to draw the foul.
Montgomery thought about taking a jumper before her pump fake sent Little into the air.
"I was going to take the shot, then I saw her jump," Montgomery said. "When somebody jumps in the air, you have to draw the foul on them, especially in that situation where the shot clock is running down."
Connecticut improved to 23-9 and moved two games ahead of Indiana atop the Eastern Conference.
Kara Lawson led the Sun with 13 points, Charles added 12, and Mistie Mims had 11 points and 11 rebounds.
Shekinna Stricklen scored 12 points to lead Seattle (13-18), but the rookie missed two shots in the final seconds. The Storm have lost four straight.
"I thought it was a great effort and we definitely put ourselves in position to win the game," Storm coach Brian Agler said. "I feel bad for our team that we didn't come through. Hand it to Connecticut. They made some plays down the stretch. They hit some free throws and made a stop when they needed to."
Tanisha Wright had 10 points and eight assists for the Storm but had seven turnovers. Little added 11 points.
Tina Thompson and Katie Smith hit consecutive 3-pointers to give the Storm a 56-54 lead with 2:21 remaining, and Smith added a 13-foot jumper to make it 58-54 with 1:22 left.
Lawson hit a 3 to cut the lead to 58-57 with 51.5 seconds left.
The Storm played without regular starters Sue Bird (strained right hip flexor) and Lauren Jackson (strained hamstring). Seattle, fourth in the Western Conference, has clinched its ninth consecutive playoff berth.
Bird missed her third straight game and Jackson her second because of the injuries. Both are listed as day-to-day with three regular season games remaining. The Storm will host Chicago on Tuesday.
Wright made two free throws early in the fourth quarter to put Seattle ahead 45-43, its first lead since 7-6 early in the first quarter.
Charles scored four straight to help put the Sun up by seven late in the third quarter. But Stricklen hit a 3 with 15 seconds left for the Storm to cut it to 41-39 at the end of the period.