LSU coach Nikki Caldwell peeked up at the scoreboard and spied an 18-point lead against Green Bay, and a somewhat odd thought wandered across her mind.

“This isn’t us; this is too soon,” she said Sunday. “We’re not that team that’s blown anybody out.”

Twelve minutes later, the curious notion nearly ended in a numbing reality after the No. 6 seed Lady Tigers fended off the 11th-seeded Phoenix 75-71 in the first round of the NCAA women’s basketball tournament at the Pete Maravich Assembly Center.

And relief could only creep in after guard Danielle Ballard, who scored a team-high 16 points, splashed through a second free throw with 4.8 seconds remaining to ensure a two-possession lead and a second-round date at 8:30 p.m. Tuesday with No. 3 seed Penn State.

“Our will to win that game shows how much we want to be here,” senior guard Adrienne Webb said. “It shows how much we’re underestimated to win this game.”

Or, perhaps, the moxie of the Horizon League champion Phoenix (29-3), who entered on a 24-game winning streak and whose largest deficit was 12 points against Cleveland State in January.

After forward Theresa Plaisance’s layup with 12:38 left gave LSU (21-11) a 54-36 lead, Green Bay’s prism reflected optimism borne out of a roster laden with five seniors and an affinity for knocking down 3-pointers.

“There’s nothing you could do at that point when you’re down 18,” said Green Bay senior guard Sarah Eichler, who scored a game-high 22 points. “You just have to band together at that moment and fight.”

Leery of a breakneck pace in the open floor, the Phoenix faced little choice in the matter of altering their persona.

“The clock just kept eating away,” coach Kevin Borseth said. “We tried to speed them up, and then we had to start going after them and doubling to create a shot as fast as we possibly could.”

Slowly, LSU, which shot 49.1 percent, saw its lead pared 65-52 with 6:41 remaining before the Phoenix, who entered shooting 35.1 percent, opened a barrage behind the 3-point arc. Forward Jenny Gilbertson, who scored a career-high 15 points in 23 minutes off the bench, buried back-to-back deep 3s, the second coming off the left wing to slice the lead to 65-58.

“It’s no surprise to us, but I guess it was a huge surprise to LSU because they weren’t guarding her and she hit those shots,” Phoenix guard Adrian Ritchie said. “It’s just about taking that role if you’re called upon.”

Reeling, LSU called for a 30-second timeout to slow the momentum.

“We’re tight right now, and we’re playing that way,” Caldwell said she told her team. “Obviously I said some other things, but it was along those lines.”

The blunt message didn’t seem to be a cudgel worth dragging out early in the second half, though. A 7-2 spurt over the closing two minutes of the first half sent LSU to the locker room leading 32-27, and Webb buried a 3-pointer from the right corner just 17 seconds out of the locker room.

Two trips later, Ballard bounced a lone dribble inside the 3-point stripe for a pull-up jumper after Jeanne Kenney drove the baseline and whipped a kick-out to the freshman.

Finally, Webb hit a 3-pointer for a 40-27 lead with 18:33 left on a fastbreak started by forward Shanece McKinney swatting Megan Lukan’s driving layup.

“I had to step up and play my role,” Webb said. “That was knocking down those shots. Our defense was on point, and when I had the opportunity to score, I had to take it.”

The jumper capped a 15-2 run over six minutes spanning the first and second halves, a stretch when the Phoenix committed five of their 15 turnovers. LSU converted the takeaways into 22 points.

“They came out and went on a huge run,” Eichler said. “It gave them the momentum. That stretch was hard to come back from.”

In hindsight, Webb said LSU knew Green Bay would make its push.

“You know they’re going to make a run,” Webb said.

So what was the consensus trudging out of the huddle and clinging to a 65-58 lead?

“You’ve got to buckle down on defense,” Webb said. “Gather your team up and say, ‘We are not going to let them score.’ ”

Instead, Eichler drilled a 3-pointer near the top of the arc to trim the lead further to points, fitting considering the Phoenix hit 12 of 28 behind the arc en route to shooting 49.1 percent.

On the ensuing possession, though, Ballard, who went 6 of 9 from the floor, knocked down a 3-pointer on the right wing with 4:41 to play.

A trip later, she curled off the right wing into the lane to take a feed from guard Bianca Lutley, scoring and forcing Ritchie, who had scored 16 points, to pick up her fifth foul.

Coolly sinking a free throw for a three-point play, Ballard extend the lead back to 71-61 with 3:05 to play.

“She’s shown this time and time again how she can change the complexion of a basketball game,” Caldwell said. “The game did not show her age. She was very composed and made some big baskets when we needed them.”

And it was enough of a cushion, too — even after Gilbertson scored inside and Eichler hit a 3-pointer to close the lead to 71-66 with 2:14 remaining.

They’d do it again 15 seconds later when Lukan hit another 3 from the left wing on a broken play to make it 72-69, but Green Bay couldn’t close the remaining space.

“Our kids really rallied and got it down to one possession,” Borseth said. “It didn’t ever look like we were going to get it there, but we did.”

LSU, meanwhile, was left with no choice but to admit the obvious.

“That final buzzer,” Plaisance said, “was such a huge relief.”