Holder Venus marches through to last 16

(CNN) -- Holder Venus Williams continued her march towards a fifth Wimbledon title by booking her place in the last 16 with a comfortable straight sets win over Spain's Maria Jose Martinez Sanchez.

Seventh seed Williams showed glimpses of her top form as she beat her world-ranked 101st opponent 6-1 7-5 in bright sunshine on Court One on Saturday.

"I was very happy with my performance," said Williams, who will play Russia's Alisa Kleybanova in the last 16 on Monday.

"Things got close in the second set, she was playing well and I needed to come up with something a little more and I was really happy to come up with that."

Martinez Sanchez began serving and volleying and charging the net in the second set and Williams added: "In the second set, it was not working for her from the back of the court so it was really impressive how she changed strategy in the second set and made it very competitive."

Williams raced through the opening set in just 25 minutes, breaking serve twice and backing it up with some powerful serving which included aces clocked at 116, 119 and 120mph.

Top seed Ana Ivanovic and former champion Maria Sharapova had already suffered shock early exits from the championships, but there was little chance of Williams suffering the same fate.

Martinez Sanchez had defeated India's 32nd seed Sania Mirza 9-7 in the final set in the second round but lacked the power to trouble Williams in any meaningful way.

She instead relied on too many drop shots against one of the fastest players on tour, and paid the price as she was broken to love in the third game of the second set.

To the 25-year-old's credit, she broke back in the eighth game and saved four break points in the next to lead 5-4, but it was merely delaying the inevitable. Williams broke again to lead 6-5 and served out in some style, finishing off with a 127mph ace.

The unseeded Kleybanova stands between Williams and a place in the quaterfinals. The 18-year-old, world ranked 42, reached the fourth round with a 6-4 6-4 victory over Japanese veteran Ai Sugiyama.

Meanwhile, fifth seed Elena Dementieva was given a tough workout by Gisela Dulko but avoided becoming another high-profile casualty.

Argentine Dulko fought hard all the way but came off second best to the Russian, going down 7-6 7-5 on Court Two.

Thai grasscourt expert Tamarine Tanasugarn continued her love affair with SW19, coming from a set down to beat New Zealand's Marina Erakovic 4-6 6-4 6-4 and she will now face second seed Jelena Jankovic.

The Serbian star had to overcome a knee injury and a determined 17-year-old Caroline Wozniacki 2-6 6-4 6-2 to advance to the last 16.

Jankovic called for treatment after winning the second set to level the match at one-set apiece.

But she broke Pole Wozniacki twice in the third, ensuring she became the only one of the top three seeded women to make the second week at Wimbledon.

It will be Tanasugarn's seventh appearance in the fourth round, although she has yet to reach the last eight.

French Open runnerup Dinara Safina struggled with a thigh injury and lost to Shahar Peer of Israel 7-5 6-7 8-6 in a three hour, 25-minute match.

Safina was up a break in the final set but, after receiving treatment, lost the lead and failed to serve out for the match. She was in tears during the final game and could only serve at half speed.

Other women advancing to the round of 16 on Saturday were 21st seed Nadia Petrova and 154th-ranked Alla Kudryavtseva, who followed her upset of former champion Marion Sharapova by beating China's Peng Shuai 6-3 1-6 6-4.