WACO, Texas -- The 13th-seeded North Carolina Tar Heels upset the No. 4 Illinois Fighting Illini 4-3 on Thursday in the Round of 16 at the lighting-and-rain-delayed NCAA Division I Men's Tennis Championship at Baylor.

North Carolina (24-10) will take on fifth-seeded TCU in the quarterfinals Saturday at the Hurd Tennis Center. Illinois completed its season with a 27-5 record. TCU blanked No. 12 Wake Forest 4-0 in the Round of 16.

A key and scrappy player for the Tar Heels was senior Esben Hess-Olesen, who won No. 6 singles 6-3, 6-2 against Brian Page, giving UNC a 2-1 lead in the match. Hess-Olesen, who hails from Denmark, has suffered from a back injury, and played in only his ninth dual match of the season. Thursday's win was his fifth victory of the campaign, and only the second since capturing a decision against Illinois in January. The Tar Heels lost the dual matchup after having match point.

Final: Virginia Highlights
Hill: UVa. secures second title in past three years
Hill: Cavaliers and Sooners to face off for title
Semifinals: Virginia | Oklahoma
Hill: Baylor with home-court advantage in semis
Hill: TCU back in semis for 1st time since 2001
Quarterfinals: Oklahoma | TCU | Virginia | Baylor
Hill: Baylor gets crack at defending champ Trojans
Hill: Hess-Olesen provides lift for UNC in upset
Hill: Southern Cal prepares to defend title
Bracket: Printable  Interactive
"It's been about two years since I hurt my back," said Hess-Olesen, whose identical twin brother, Soren, plays for Texas. "I herniated a disc and my joints became inflamed."

The economics major clinched the NCAA second-round match against 20th-ranked Mississippi State on May 9, which propelled the Tar Heels to a berth in the final 16. Prior to that, Hess-Olesen had not played singles since retiring against Duke on April 9.

"It feels great to be out there again," said Hess-Olesen, who received an invitation to the 2013 NCAA Singles Tournament. "I just told myself to play my game and push through. We had a game plan ready for me, and I stuck to it. We were really motivated to come out here and fight as much as we could."

Hess-Olesen and Brayden Schnur teamed up and won No. 1 doubles, beating the Illinois team of Jared Hiltzik and Tim Kopinski 8-5. The Tar Heels won No. 3 doubles and led 1-0 in the spirited match. Schnur tied the match at No. 1 singles, out battling Farris Gosea 7-6, 2-6, 6-4. Then came the clincher by Ronnie Schneider at No. 2 singles. Schneider emerged as the winner against Hiltzik 7-6, 4-6, 6-3.

North Carolina coach Sam Paul credited Hess-Olesen for his fighting spirit, which permeated throughout the team.

"When he clinched the match against Mississippi State, we were all in tears," Paul said. "Two years ago, he was ranked No. 23 in the country, and was the leader of our team. He later was at the doctor and back specialist every week. Most kids would just quit. He saved the best for last. That was a lesson for all of us."

Top-seeded Oklahoma survived a scare from No. 16 UCLA, beating the Bruins 4-3, which began outdoors and moved indoors with the weather delays. Oklahoma, last year's runner-up, faces No. 8 Georgia in Saturday's quarterfinals. The Bulldogs bested No. 9 Texas 4-1, which was also completed indoors. No. 3 Virginia was a 4-0 winner against Columbia in the only other completed match.

No. 6 Texas A&M and 11th-seeded Ohio State were moved indoors to the SMU campus in Dallas. Defending champion Southern California, seeded seventh, played No. 10 Duke in a night match. Second-seeded and host Baylor also played under the lights, taking on South Florida.