DOHA: Danish teenager Caroline Wozniacki overcame crippling cramp to reach the WTA Championships semifinals on Thursday defeating Russia’s late call-up Vera Zvonareva 6-0, 6-7 (3/7), 6-4.

Wozniacki ended the 2hr 48min match in tears after collapsing to the court in agony, clasping her left thigh, when she was just two points from victory.

But world No. 9 Zvonareva, the runner-up in 2008 and who was summoned to the $4.55 million event after Dinara Safina withdrew on Wednesday, failed to take advantage, allowing the Dane to secure an emotional win.

Wozniacki could have had the tie wrapped up when she led by a set and 5-2 before wasting two match points in the 12th game.

The 25-year-old Zvonareva battled impressively, overcoming a nasty courtside nosebleed in the second set.

For the second consecutive evening, the 10-minute heat rule was invoked after the second set, allowing the players to recover from the 33-degree heat and crushing humidity.

On their return, Wozniacki led 3-1 but was pinned back to 3-3 before needing treatment on her bandaged thigh.

But with the tie seemingly slipping away, she bravely broke to lead 5-4 before claiming victory when Zvonareva netted a forehand.

Youzhny pulls out

In St. Petersburg, top-seeded Mikhail Youzhny of Russia retired with lower back pain while trailing Denis Istomin of Uzbekistan 6-2, 2-1 Thursday in the second round of the St. Petersburg Open.

Trailing 5-2, 30-15 on his serve in the first set, Youzhny double-faulted. He saved one set point but then returned wide to loose the set. He took a medical time out to have his back massaged but trailing 2-1, 15-40 in the second set he decided to retire.

Cilic stays on target

In Vienna, top seed Marin Cilic revved up a bid for possible inclusion in next month’s season-ending ATP final as he reached the quarterfinals with a 7-6 (9/7), 6-4 defeat of German Daniel Brands at the Austria Tennis Trophy Thursday.

Cilic is among ten men chasing the last two places in the World Tour Finals in London from Nov. 22.

The Cilic victory was his 42nd of the season against 18 losses and a title in early January in Chennai.

Ljubicic in quarters

In Lyon France, third-seeded Ivan Ljubicic of Croatia reached the quarterfinals of the Lyon Grand Prix on Thursday by beating Nicolas Kiefer of Germany 6-3, 3-6, 6-3.

Ljubicic served 27 aces and broke his opponent twice to extend his perfect record against Kiefer to 4-0.

The 30-year-old Ljubicic will face Florent Serra of France in his eighth quarterfinal of the year.

Also, former Lyon finalist Marc Gicquel of France upset Paul-Henri Mathieu 6-4, 6-0.

The sixth-seeded Mathieu was hampered by cervical pains and lost his serve five times.

It’s probably my best match so far this season.”