Serena Williams beats Bertens to make French Open final

Defending champion Williams, who won the first of her three Roland Garros crowns in 2002, started slowly for the second day running, her early play littered with the unforced errors that had characterised Thursday's laboured three-set quarter-final win against Kazakh Yulia Putintseva.

The champion was broken in the first game by her unseeded opponent who, entering the contest on a 12-match winning singles streak in all competitions, showed no sign of nerves in her first major semi-final.

"The first set was not very easy but I think that today I played better. (Bertens) played very well," Williams said courtside.

The defending champion got off to a poor start and fell a break behind, with Bertens looking likely to claim the opening set as she led 5-3 - and at the time the American looked in trouble with injury.

But Serena battled to a tie-break, in which she saved two set points before claiming the opening set.

Bertens broke early in the second set, but Serena broke back quickly and then never looked back as she grabbed control of the match.

The Dutch player saved three match points as she served while trailing 5-3, but clung on to make the defending champion serve it out as Bertens hit a forehand long on the fourth match point.

Serena closed out a 7-6(7) 6-4 victory - but the physical struggles she appeared to be going through makes it far from certain that she will defend her title when she returns to Court Philippe Chatrier on Saturday afternoon.

If she does so, however, the prize is great: not just a fourth French Open title, but also a 22nd Grand Slam title to equal the professional-era record set 17 years ago by Steffi Graf at this very same venue.