Although the Tar Heels (21-3) controlled the ball for much of the match, two key lapses on one play allowed Indiana (16-6) to seize the lead.
The series started when Indiana striker Pat Noonan stole a weak pass by UNC midfielder Michael Bucy. Noonan then lofted a ball from midfield to the right side of the penalty area for a streaking Mack.
Mack, the Big Ten player of the year, collected the pass after sneaking by UNC's Eddie Robinson. Mack fired a shot past goalkeeper Michael Ueltschey to the near post for the game-winner.
"I took my eye off my man for two seconds and watched the ball," Robinson said. "And they scored a goal, and that's the way it is, especially at this level against Indiana. You can't watch the ball - they're just too good."
The goal was in stark contrast to a foul-heavy, plodding first half. UNC and Indiana combined for six shots before the break as both teams dealt with the rain-soaked condition of the field.
But the Indiana goal sparked an offensive revival in the Tar Heels. Much as he did in first- and second-round matches, Bolowich inserted 6-foot-5 Matt Laycock and 6-3 Ryan Kneipper to try to play a more direct game of sending flank passes into the penalty area.
"I thought they sent their basketball team out there in the last 20 minutes," said Indiana coach Jerry Yeagley, who won his 494th career match. "They just kept getting bigger and bigger, and we didn't have any answers to their size. When they play direct to those big guys, you just have to hang on. And that's what we did."
Indiana did hang on, barely. In the 63rd minute, Hoosier goalkeeper Colin Rogers made a lunging save at the left post to stop a Chris Carrieri head ball.
In the 70th minute, the Tar Heels had another chance to tie the match, but Laycock's header from 4 yards out was cleared from the goal line by Indiana midfielder Tyler Hawley.
For the rest of the match, UNC continued to have opportunities against a bunkered Hoosier defense that featured eight or nine players behind the ball. The Tar Heels had eight corner kicks, all of which came in the second half.
"I was convinced that we would score," Bolowich said. "I was convinced that we would pull it out. The chances we did create were legitimate chances right in front of the goal."
Laycock had perhaps the Tar Heels' best opportunity to score with less than three minutes left. He settled a Bucy pass near the penalty mark, but his straight-on shot from 8 yards out sailed over the Indiana goal.
To get the day's news and headlines in your inbox each morning, sign up for our email newsletters.
"(Indiana is) not interested in opening up and playing an entertaining match at this point in the season - they're looking for the result," Bolowich said.
"They were looking for the one or two chances where we wouldn't be paying attention or when we would be unbalanced defensively. And they got that, and they made the most of it."
The Sports Editor can be reached at email@example.com.