By Martyn Herman

LONDON (Reuters) - Champion Serena Williams safely negotiated another 107 minutes of her comeback as she settled back into the old routine with an ultimately comfortable 3-6 6-2 6-1 victory over Simona Halep in the second round of Wimbledon Thursday.

The American seventh seed, just four matches into the most challenging return of her career after injury and serious health issues sidelined her for 49 weeks, was initially troubled by the tenacious Romanian teenager before marching on.

Dispatched to Court Two, the atmospheric sunken bowl in the heart of the All England Club, the 29-year-old resembled a powerful sports car desperate for some open road in the early stages as Halep's accuracy had her stuck in first gear.

Despite being largely outplayed in the opener, there was never a sense of panic though and once she stemmed the flow of errors, began middling her forehand and booming down her mighty serve there was only ever going to be one outcome.

"I feel like I'm in shape," the American, who lacerated her foot on broken glass in Munich last year just weeks after beating Vera Zvonareva in the final here, told reporters. "I'm just playing my way into match condition.

"I'm just doing things that I did before. That's all. That's all I can do right now."

More used to playing her matches on the enclosed surroundings of Center Court, Williams took a while to find her range as the wind swirled and dark clouds loomed above the snug 4,000-seater arena.

She later shrugged off being made to walk the aisles to Court Two although admitted she "hated" its predecessor, dubbed the Graveyard of Champions.

"I'm like, okay, this gets my legs moving, Williams said when asked about the court scheduling. "They like to put us on CourtTwo, me and (my sister) Venus, for whatever reason.

"I haven't figured it out yet. Maybe one day we'll figure it out. At least now they have a (Hawkeye) out there, so I do like that. It was much better than the old one that was actually closer. I really hated that court."

After a rare show of emotion on Center Court following her win over Aravane Rezai on Tuesday, it was a much calmer Williams against the 58th ranked Halep who was playing in the Wimbledon main draw for the first time.

While the 19 unforced errors she committed will be a minor concern, she was swinging cleanly off both wings as the match wore on while her serve was dominant with nearly 90 percent of successful first deliveries earning her the point.

Halep began with real intent, however, and capitalized on some wayward play from her opponent to break for 3-1 when a Williams backhand whistled over the baseline.

Leading 5-2, Halep slipped on the slick grass while pushing off to return a serve and gingerly held her knee, signaling immediately for the umpire to summon a trainer.

However, it did not appear to effect her level and another Williams backhand error gave her the first set.

Former French Open junior champion Halep, who had breast reduction surgery in 2009 to help her mobility, received lengthy treatment at the end of the set while Williams put back on her white cardigan and limbered up near the umpire's chair.

Once play resumed the match quickly turned Williams' way.

Halep suddenly began hitting the net with her groundstrokes and Williams needed no second invitation to seize control.

Williams squandered three match points at 5-0 in a one-sided third set but made no mistake in the following game when she powered down a first serve to end the contest and book a clash with 26th seed Maria Kirilenko.

Only once has Williams not reached the third round of a grand slam in 44 appearances and after again reaching that stage she appeared to have her teeth into the tournament, although she would prefer some faster starts.

"I definitely feel like I started slow today," the 13-times major champions said. "I was actually really, really trying to start out fast but I also think that I got a little tight out there and I just need to relax."

(Editing by Mark Meadows and Pritha Sarkar)