By John Stonestreet

LONDON (Reuters) - Two young German-speaking pretenders to Novak Djokovic's tennis crown took further small steps on Wednesday toward the goal of dethroning him, comfortably seeing off experienced opponents at Wimbledon as they advance steadily up the rankings.

While Serbian Djokovic, reigning supreme at the top of the game with four consecutive grand slam titles, was sweeping past France's Adrian Mannarino in the luxurious setting of Centre Court, 22-year-old Austrian Dominic Thiem had to battle the elements as well as Germany's Florian Mayer on Court 3.

For eighth-seeded Thiem, whose French Open run earlier this month was ended at the semi-final stage by the undisputed world number one, Wednesday's match -- on a surface he has viewed with suspicion -- nudged him another rung up the career ladder.

Unseeded Mayer, 32, beat the Austrian on grass last week in the semi-finals of the Halle tournament, but this time

Thiem took revenge, mixing his trademark whipped groundstrokes with dropshots and deft volleys for a smooth straight sets win.

"I had to concentrate very hard. Had I let my level drop things would certainly have ended badly so I am really happy to have made it through," Thiem told reporters.

His match lasted one hour 37 minutes -- exactly the time it took 19-year-old German Alexander Zverev, seeded 24, to demolish French veteran Paul-Henri Mathieu for the loss of just nine games on Court 16.

Ranked 136 at the start of 2015 and at a career-high 28 in the run-up to Wimbledon, Zverev has tracked Thiem for much of the season.

Friends off court but having never met in earnest on it before this year, the pair have clashed three times in Zverev's past five tournaments.

The German has yet to emerge victorious but has grabbed a set on each occasion as well as scoring a maiden win over Roger Federer in the other Halle semi-final, suggesting he will also break his duck against Thiem before too long.

The Austrian, meanwhile, ranked just one place below his peak of seventh, also scored his first grasscourt victory over Federer -- and his second in all -- in winning the Stuttgart tournament the week before Halle.

But despite that success over the seven-times Wimbledon winner, for Thiem -- who described cementing his place in the top 10 as his "next big goal" -- reaching his comfort zone on grass remains very much a work in progress.

"Of course I would love to progress (at Wimbledon) but if I lose tomorrow or on Friday it wouldn't be such a big deal as losing in Paris (on clay)," he said.

"I don't think I'd be viewed as favorite against anyone on grass and that's exactly how I see it."

(Editing by Martyn Herman)