Freshman Kirk Urso scored in the 61st minute to send UNC to the final four for the first time since winning the 2001 national title.
"It was exactly the game we expected and the opponent we knew we would get, tough defensively and very strong," said UNC coach Elmar Bolowich. "They didn't give us anything and didn't make any mistakes. We had a hard time again getting the rhythm going. In the second half we regrouped, our attacking strategy paid off, and we had more looks at the goal. We felt like we needed one goal to break the ice and we got it."
After a Carolina corner kick, Michael Callahan served the ball from the left side into the box. It was chested down by a Wildcat defender, and Urso volleyed home the loose ball from 15 yards out.
The goal was just the 13th allowed by Northwestern all season and just the second in four NCAA matches.
Urso, a native of the Chicago suburb of Lombard, scored for the second straight game against a team from his hometown. After missing four straight games due to injury, Urso netted Carolina's first score in the third round against UIC.
"It's always about fighting to find the right spot and being in the right spot at the right time and lucky enough it took a good bounce for me," said Urso, who has 12 points on the year. "[Billy] Schuler, my roommate, let it go, and I was right there and buried it and it went in. It's like a dream right now. We've worked so hard. Our team, we knew we had the potential the whole year. For this to be happening at this time it's just amazing, it's just a dream."
The loss ended Northwestern's season in the quarterfinals for the second time in three seasons.
"I'm very proud of our guys," said Northwestern coach Tim Lenahan. "Not just for this year but for this group of seniors, they're the winningest group in school history and they've done a great job. It came down to one play, and North Carolina is a very talented team, but I thought we played a great game."
Dec. 6 in Chapel Hill, N.C.
North Carolina 1 Northwestern 0. Goals: Urso 61.
North Carolina -- Haggerty, Loyd, Graye, Williams, Adeleye, Callahan, Lewis, Brown, Ababio, Schuler, Shriver. Subs: Urso, Rodriguez, McCarty.
Northwestern -- Rosenthal, Coleman, Ratner, Stanley, Usinger, Blades, Voigt, Fallon, Bellizzi, Pett, Eliason. Subs: Kupe, Valenta, E.O'Neill, Hillgard.
Referee: Lou Labbadia.