NEW YORK—Front-row fans veered back and forth like airplane passengers tossed around during turbulence. Milos Raonic's volatile serve provoked a visceral reaction from the crowd, but kept the Canadian calm during a sometimes wild ride into the U.S. Open third round.

Raonic launched 26 aces and played his most assertive tennis in the tiebreakers to tame qualifier Peter Gojowczyk, 7-6 (4), 5-7, 6-4, 7-6 (3), in a high-octane clash on Louis Armstrong Stadium.

Don't let Gojowczyk's triple-digit ranking and qualifier status fool you: The 124th-ranked German is a dangerous player who packs a punch on serve, can crack the ball down the line off both wings, and deaden angled volleys. There's a fearlessness about Gojowczyk that makes him fun to watch. A couple of times he hit drop volleys that elicited ran-down replies right toward the rib cage of the man from Munich, who stood his ground at net and blocked back winning volleys. But Gojowczyk's skill set shouldn't have surprised Raonic: He beat the big man in straight sets on grass in Halle this June, just weeks before Raonic's run to the Wimbledon final four.

The No. 5 seed carried a 24-9 tiebreak record into the first-set breaker and his comfort level in extra sessions was crucial. Down 3-4, Raonic answered with an ace, followed with a forehand winner, and sealed the first set chipping a short forehand return that surprised his opponent. It drew the error to seal the 52-minute opener and prompt chants of "Milos! Milos!"

Sporting the samurai-style hair reminiscent of a young Xavier Malisse, Gojowczyk responded with some timely returns and fine work around net. He broke twice and won nine of 11 trips to the front court, snatching the second set to level and earning some support from a small but enthusiastic group of fans chanting "Let's Go Gojo!"

There was a time when Raonic predictably played the inside-out forehand in an effort to hit through opponents. He mixed his shots more effectively on critical stages tonight, hitting short-angle slice backhands, spreading the court with the inside-out forehand and then sometimes blasting his flat forehand down the line to finish points. The confidence to unload on both first and second serves makes Raonic an explosive presence: He blasted a menacing 130 M.P.H. missile down the middle to end the third set with a bang.

Gojowczyk wasn't about to go quietly into the night. On the full stretch, he guided a forehand return winner down the line to reach triple break point in Raonic's opening service game of the fourth set. That stunner was a prelude to the brilliance that followed. Gojowczyk blocked a skipping half-volley winner that spun sideways before dying beneath the chair umpire's seat to break for a 2-0 fourth-set lead. He failed to back up the break, however, lining a double-fault into the tape as Raonic broke back.

The 25-year-old withstood a pair of break points in both the seventh and ninth games, but he blinked in the tiebreaker opening with a double fault. Cranking up his serve, Raonic slammed a service winner and pair of aces to stretch his lead to 5-1. On his third match point, he plastered a 130 M.P.H. serve winner down the middle to close a three hour and six-minute battle, pounding his first over his heat to punctuate it.

"The most important thing was I showed courage at the end and started going for it," said Raonic afterward. "There was a few hours maybe missing that so I'm glad I turned it around and glad I won."