* Russian Youzhny to face world number two in last 16
* Australian Tomic knocks out ninth seed Gasquet
* British teenager Robson keeps home flag flying
* Top seeds Djokovic and Williams due on court later (Adds later matches)
LONDON, June 29 (Reuters) - Russian Mikhail Youzhny loomed on Andy Murray's horizon and Australian Bernard Tomic hurtled back on to the grand slam radar as an unpredictable Wimbledon neared its halfway point on Saturday.
Youzhny, the 20th seed, beat Viktor Troicki in straight sets to reach the last 16 while bad-boy Tomic continued his impressive form to knock out French ninth seed Richard Gasquet.
Tipped as his country's next big thing the 20-year-old Tomic has instead gained a reputation as a sports car-driving playboy and was left out of Australia's Davis Cup team last year for what officials considered a lack of effort.
A quarter-finalist here in 2011, Tomic had lost his last 11 matches against top-10 opponents but produced a display of maturity and skill to win 7-6(7) 5-7 7-5 7-6(5).
Youzhny's clash with Serb Troicki at a sun-drenched All England Club was one of four men's third round matches in the lower half that had been held over from a rain-hit Friday.
In the others, Spain's Fernando Verdasco, Poland's Lukasz Kubot and Frenchman Kenny De Schepper also reached the last 16.
Yet another injury blighted the tournament with Dutchman Igor Sijsling's retirement from his third round match with Croatia's Ivan Dodig taking the tally of withdrawals to 13 - already equalling the previous worst toll in 2008.
Apart from appearing on Centre Court in a parade of Britain's Olympians, Murray enjoyed a day of leisure having seen off Spain's Tommy Robredo under the Centre Court roof on Friday.
With the hype beginning to boil as he tries to go one better than last year and become Britain's first male Wimbledon champion for 77 years, the world number two would have enjoyed seeing Laura Robson win to keep him company in the second week.
The unseeded 19-year-old rallied from the brink of defeat against New Zealander Marina Erakovic to win 1-6 7-5 6-3, sparking wild celebrations on Court Two and on the slope known as Henman Hill where thousands watched on a huge screen.
There was disappointment, though, for a legion of Japanese fans watching 12th seed Kei Nishikori as he went down in five sets to Italian Andreas Seppi after twice being in front.
Number 23 seed Seppi has now prevailed in his last seven five-set matches.
Japan's hopes in the singles now rest on the ageing legs of 42-year-old Kimiko Date-Krumm who has the formidable challenge of trying to stop defending champion Serena Williams later.
Former women's champion Petra Kvitova avoided becoming yet another high seed to perish as she completed a third round victory against Ekaterina Makarova over two days.
The eighth-seeded Czech, champion in 2011, returned to court 2-1 down in the final set after bad light and drizzle stopped play on Friday and revelled in Saturday's warmer temperatures to take the deciding set 6-3.
American Sloane Stephens moved away from the abyss against lowly-ranked Czech Petra Cetkovska to reach the fourth round at Wimbledon for the first time where she will face another last-16 debutant in Puerto Rican Monica Puig.
In a match that was also completed over two days, the 17th seed lost eight games in a row after winning the first set on Thursday in a tiebreak, but from 2-0 down in the deciding set she pulled herself together to win it 6-4.
Another American tipped for a bright future, teenager Madison Keys, was also seeking a last 16 berth but lost out in three sets to Poland's fourth seed Agnieszka Radwanska, who faces Bulgaria's Tsvetana Pironkova in the last 16.
Youzhny served notice that Murray's expected charge into the final for a second consecutive year will not be the cakewalk some predict in the wake of a rash of first-week retirements and withdrawals that decimated the bottom half of the draw.
The burly Russian won 6-3 6-4 7-5 but inevitably most of the questions in his news conference revolved around his impending battle with home favourite Murray.
"Don't worry, I will sleep normal," Youzhny said, when asked if he was concerned about being public enemy No.1 on Monday.
Top seed Novak Djokovic, the man seen as the biggest hurdle to Murray, faces Frenchman Jeremy Chardy later on Saturday having not dropped a set in his first two rounds. (Reporting by Martyn Herman; editing by Ken Ferris)