Serena on a roll as she roars into Wimbledon last 16

Seven-time champion Serena Williams moved ominously into the last 16 at Wimbledon when she recovered from a sluggish start to beat France's Kristina Mladenovic 7-5, 7-6(1) on Friday.

The American, seeded 25, looked sluggish initially and trailed 5-3 but the 36-year-old flicked the switch and reeled off six games in a row as Mladenovic wilted in the heat.

To her credit Mladenovic recovered her poise and had a chance to break the Williams serve at 4-4 in the second set.

Williams slammed the door shut though and piled on the pressure when Mladenovic served at 5-6.

Mladenovic saved one match point with a graceful forehand winner and forced a tiebreak but there was no stopping Williams as she steamed through it like an express train.

She brought up another match point with a 12th ace and finished it off with her 13th.

Williams has now won 17 consecutive matches at Wimbledon including the 2015 and 2016 titles.

She missed last year's tournament because she was pregnant with daughter Alexis Olympia.