* Sharapova finishes strong to reach last eight
* Top seed Azarenka cruises through
* Third seed Radwanska goes out (Updates with Wozniacki win)
By Mark Lamport-Stokes
INDIAN WELLS, California, March 12 (Reuters) - Former champion Maria Sharapova raised her game when it mattered to storm into the BNP Paribas Open quarter-finals with a 7-5 6-0 victory over Spaniard Lara Arruabarrena-Vecino on Tuesday.
Australian Open champion Victoria Azarenka also cruised into the last eight, pounding Poland's Urszula Radwanska 6-3 6-1 in a match lasting just under 90 minutes despite being hampered by a sore ankle.
Fifth seed Petra Kvitova advanced with a comfortable 6-2 6-3 win over fellow Czech Klara Zakopalova but third seed Agnieszka Radwanska of Poland was knocked out, losing 6-1 4-6 7-5 to 13th-seeded Russian Maria Kirilenko.
Russian world number three Sharapova won a tight opening set then swept through the second in only 22 minutes to reach the quarter-finals at the Indian Wells Tennis Garden for a third consecutive year.
The second seed will next meet Italy's Sara Errani, a 6-3 6-2 winner against Frenchwoman Marion Bartoli earlier in the day, in a re-match of last year's French Open final clinched by the Russian.
"I stepped up my game in the second set," Sharapova, who was champion here in 2006 and a losing finalist last year, said courtside after wrapping up victory in one hour 18 minutes.
"The first set was so up and down I had to buckle down, stepping into the returns and getting in a few more first serves. It was a slow start. Just didn't get a good rhythm on her game from the beginning.
"I think maybe I was going for the lines a little bit more than I had to, especially in the first few games when you don't know too much about your opponent or haven't played her."
Sharapova had never previously played against the 20-year-old Arruabarrena-Vecino, who is ranked 87th in the world and won her first WTA singles title in Bogota last year.
There were five breaks of serve in an erratic opening set but the Russian earned the crucial break in the 11th game when her opponent pushed a forehand wide.
Sharapova needed three set points before serving out, then broke Arruabarrena-Vecino's serve three more times in the second set to advance with ease.
Top seed Azarenka, who initially struggled to find her rhythm before battling past Belgian Kirsten Flipkens 3-6 6-3 6-0 in the previous round, broke Radwanska's serve three times in the opening set and twice in the second.
"I wasn't feeling that well," said the Belarusian, who is bidding to become the first woman to successfully defend the WTA title at Indian Wells since Martina Navratilova in 1991.
"My ankle was bothering me, it's been bothering me for a while. But, on the bright side, I won the match. I could overcome those things.
"I decided to just take everything in my own hands and see where it takes me."
Asked whether her ankle problem could force her to withdraw from Indian Wells, Azarenka replied: "I'm not going to give any answer of pulling out, that's for sure.
"I'm going to do everything I can to be ready for my next match and fight as hard as I can."
Azarenka, who is unbeaten in 17 matches this season, will face eighth-seeded Dane Caroline Wozniacki in the quarter-finals. Wozniacki, the 2011 champion here, beat Russian Nadia Petrova 7-6 6-3 in the fourth round. (Editing by Peter Rutherford/Amlan Chakraborty)