Ashleigh Barty advances to US Open third round; Jason Kubler forced to retire

Serena cruises in Round 2 to set up all-Williams showdown (0:23)

Serena Williams defeats Carina Witthoeft 6-2, 6-2, as she advances to the third round to face off against sister Venus Williams. (0:23)

Ashleigh Barty has overcome a bizarre mid-match stoppage to safely advance to the third round of the US Open for the second straight year.

Barty's cunning court craft and clutch serve was too much for Lucie Safarova, Australia's top-ranked player taking out the former French Open finalist 7-5 6-3 under lights on Show Court 17 at Flushing Meadows.

In setting up a likely third-round clash with Spanish superstar Garbine Muguruza, Barty had as much trouble dealing with a malfunction with the on-court PA system as she did with her classy but erratic Czech opponent.

The 18th seed blasted 10 aces and won 86 percent of points after landing her first serve while breaking Safarova three times either side of a strange noise disturbance late in the first set.

Play was halted for more than seven minutes as an unnerving sound bellowed through the PA system immediately after Barty was broken while trying to close out the set at 5-3. The two players - as well as fans in the stands - spent much of the interruption with their fingers in their ears as officials worked frantically to rectify the problem.

"It was very strange. I don't think Lucie and I have ever come across anything like that before," a bemused Barty said.

The pair could barely hear the tournament referee trying to explain the seemingly unexplainable during the hold-up.

When play finally resumed, Safarova held to love to draw level at 5-5 only to drop serve in the 12th game with a flurry of unforced errors to hand Barty the first set. It was one-way traffic in the second as Safarova's mistake-rate mounted, leaving Barty to prevail on her third match point.

Barty's victory came on a day of drama and disappointment elsewhere for her compatriots.

Luckless battler Jason Kubler was cleared of a broken ankle after suffering another shattering injury blow at the US Open. The 25-year-old was sent to a New York hospital after being forced to retire from his second-round match against American young gun Taylor Fritz after rolling his ankle late in the third set.

Kubler had been closing in the hunt for the most significant win of his stop-start career before disaster struck and, unable to serve or run, he reluctantly called it quits while trailing 6-3 3-6 6-3.

After fighting back from a break down in the set to be holding game point serving at 3-4, Kubler crumpled to the court in despair. His right foot got stuck in the sticky cement surface while reaching for a forehand on another baking hot day at Flushing Meadows.

After several minutes of treatment from the tour physio, Kubler received generous applause from the crowd as he hobbled to his changeover chair to have the ankle taped.

He gamely played on but, immediately upon the resumption from his medical time-out, the Queenslander hit two weak forehand errors to gift Fritz a break before the American closed out the set as Kubler walked gingerly back to his chair.

With the US Open's new heat rule in effect, the two players opted to take a 10-minute break. But it didn't help, with Kubler playing only two points of the fourth set before conceding.

Kubler's latest crushing blow comes two days after he savoured his first-ever win at a grand slam after waiting eight years between majors due to six rounds of knee surgery.

The former world No.1 junior was already assured of a career-high pay day of $127,000 for reaching the second round. A win over Fritz would have earned Kubler at least $213,000.

Instead, he must settle for a projected rankings rise to a career-best No.90 in the world after languishing at 945th this time last year.