By Ossian Shine

LONDON (Reuters) - Rip up the rankings. Form is temporary, class is permanent.

While the giggles are gone and the gymnast's genes less evident, that hooked, looped, whipped, thumped forehand stole the show at Wimbledon on Wednesday as Kim Clijsters, on her valedictory tour, barged into the third round.

It was fitting that it should be a shoulder-height crunched forehand which sealed her passage - the shot creating a sonic boom amplified by the closed roof on center court.

Clijsters is bouncing in the basement of the world's top 50 these days, but come grand slams her quality is at the fore, and on a drizzly, overcast South-west London evening Andrea Hlavackova was relegated to bit-part actress as the Clijsters circus rolled on.

Her demeanor has been matured by marriage, motherhood and the passing years, and it was a muted joy which heralded her 6-3 6-3 victory - a clenched fist and a determined nod rather than a skip and giggle.

"Yeah, I was very happy with the way everything went today," the 29-year-old winner of four grand slam titles said.

"I felt it was another step upwards from my first match against (Jelena) Jankovic. I was really focused once I got out there and just really tried to be ready from the start."

Clijsters, a former semi-finalist here, has said she will walk away from tennis after August's U.S. Open, and dominated from the off on Centre Court.

She is too long in the tooth to get carried away, however. "I was able to just keep my level up throughout that whole match," she said flashing a smile, before switching to Flemish.

(Editing by Pritha Sarkar)