Daniel Byrnes knows his brother very well.

And it didn’t take the Australian long to learn a thing or two about Denver’s Benny Althaus on Saturday.

Nathan Byrnes, the younger brother of Daniel, a senior on last season’s Oklahoma State tennis team, closed out a 4-6, 6-4, 6-3, victory to give the Cowboys a nail-biting 4-3 win in the first round of the NCAA Tournament at Michael D. Case Tennis Center.

Nathan, a junior, won the last 12 points on his serve in the third set.

“I probably wouldn’t have won if my brother hadn’t helped me so much,” said Nathan Byrnes, whose brother was courtside during the match. “He’s always been really good about finding players’ weaknesses and he pretty much told me where to serve that entire third set. He’s great with service patterns, trying to fool the person you are playing.

“It was a little bit nerve-racking because I haven’t closed out that many matches. But I’ve always stayed pretty calm on the court.”

Denver’s Pioneers, making their first NCAA appearance under second-year coach Danny Westerman, provided plenty of competition. After O-State earned the doubles point, DU (18-7) won the first set in four of the six singles matches.

“I don’t think we were thinking about Tulsa,” said OSU sophomore Oleksandr Nedovyesov, the nation’s third-ranked player. “We knew (Denver) was going to be good. The doubles point was very big for us and it was difficult to play in the wind.”

“There is such a small margin for error,” said O-State coach James Wadley.

“That doubles point … it’s so big and it turned out that way (Saturday). A point here, a point there … things could have been different.

“For Anton (Bobytskyi) to come back the way he did in singles after getting injured was big and (Nedovyesov) really beat a good player. And Nathan really played well when we needed it.”

Nedovyesov and Nathan Byrnes, ranked 18th, edged 10th-ranked Adam Holmstrom and Niklas Persson, 8-5, at No. 1 doubles.

Ivan Puchkarov and Dmytro Petrov turned a close No. 2 doubles match into a rout, beating Andrew Landwerelen and David Simson, 8-3.

Bobytskyi, a freshman, suffered a cut on his left hand during the No. 3 doubles match when, hustling for a lob, he ran into the court’s scoreboard.

“There was a lot of blood,” Bobytskyi said. “It was my left hand, so it was OK, I guess.”