Quick, who has a longer current winning streak at the U.S. Open Tennis Championships — Roger Federer or Jack Sock?

Federer may hold the record for Grand Slam titles, but the 19-year-old Lincoln native has him beat in this particular category. At least right now.

Sock ran his winning streak in three different events to nine straight matches with a pair of victories Thursday at the Billie Jean King National Tennis Center in Flushing Meadows, N.Y. First, Sock overpowered Italy's Flavio Cipolla 6-2, 6-2, 6-4 to advance to the men's singles third round.

Later, Sock and American Melanie Oudin began defense of the mixed doubles crown they won at last year's Open with a 4-6, 6-3, 1-0 (15-13) come-from-behind win over fifth-seeded Katarina Srebotnik of Slovenia and Nenad Zimonjic of Serbia. Sock and Oudin erased two match points against them in the match tiebreaker to advance.

That's their sixth straight mixed doubles win spanning back to last year. On Tuesday, Sock and American Steve Johnson upset the men's doubles top-seeded team of Max Mirnyi and Daniel Nestor 1-6, 7-6, 6-2 in the first round.

"I haven't felt nervous in a tennis match for a long time," Sock said. "I don't know what it is, but I think it's a pretty good attribute for me and a pretty good thing for me to have. I feel comfortable where I am, feel confident. I think it shows on big points."

Sock cranked 15 service aces and 41 winners in avenging a 6-3, 6-1 loss to the No. 87 ranked Cipolla in the first round of the Farmers Classic in Los Angeles last month. Sock converted all six break points he had on Cipolla's serve and consistently served his way out of trouble, saving 12 of the 13 break points he faced.

Sock won nine straight games at one point, going from a 2-2 deadlock in the first set to a 6-2, 5-0 lead. Sock finally broke Cipolla for the final time to go up 5-4 in the third set, then he saved two break points on his own serve to close out the match.

"In LA, I was pretty impatient, playing too risky," Sock said. "Today I was a little more patient, waiting for the right ball to attack, be aggressive, and I think it worked out pretty well."

Sock will face 11th seeded Nicolas Almagro of Spain in the third round. It will be his first test against a top 20 player in this year's tournament.

"I think it's just matches and experience," said Sock when asked about what separates him from the top 20 players. "Obviously I can always improve my game, improve the physicality, the shape I'm in. As long as I keep doing that, I think I can get there."

Reach Ron Powell at 402-473-7437 or rpowell@journalstar.com.