Serena Williams took the long route through to round three at the French Open as the veteran battled past Romanian Mihaela Buzarnescu.

The American waved the chequered flag at the Monaco Grand Prix 10 days prior to this clash, but there will be no white flag in Paris yet from Williams who dug deep for a 6-3 5-7 6-1 win.

Three times a Roland Garros champion, Williams continued her search for more title-winning form on Court Philippe Chatrier, and a tricky clash with compatriot Danielle Collins will be next for the 39-year-old.

This win improved Williams' second-round record in grand slams to 74-2, her only defeats at this stage having come against sister Venus Williams when Serena made her debut in the majors at the 1998 Australian Open, and against Garbine Muguruza seven years ago at this tournament.

Williams controlled the opening set against Buzarnescu, but the Romanian world number 174 was a wily opponent and began to ask plenty of questions of the 23-time grand slam winner.

Having been as high as number 20 in the rankings, Buzarnescu was not intimidated. In 2018, she beat top-10 players Jelena Ostapenko and Elina Svitolina – twice, in Svitolina's case – and the 33-year-old broke to lead 4-2, with Williams recovering from 0-40 before netting a forehand followed by a backhand as the pressure told.

Williams broke back, yelling "Come on!" to rally herself, and she had two break chances again at 5-5, but could take neither.

Buzarnescu was the first to have a set point and an eye-catching cross-court backhand forced the decider.

Tension briefly filled the air but it soon drifted away, Williams taking command with an immediate break followed by another to lead 4-0, the decider going her way emphatically.

"She has a lot of skills," Williams said of Buzarnescu. "She plays really well on this surface in particular. I knew it wasn't going to be easy, but I'm excited to get through there. It was good competition."

DATA SLAM: LUCKY NUMBER SEVEN?

Williams lives to fight another day and perhaps a good workout will give her the confidence to come through battles that lie ahead. That record-equalling 24th slam remains a possibility this fortnight. Collins is next, a player Williams narrowly beat when they met at the Yarra Valley Classic in Melbourne earlier this year, their one previous meeting. Serena has won two of her previous grand slams as the seventh seed before – at the 1999 US Open and the 2005 Australian Open.

WINNERS/UNFORCED ERRORS
Williams – 26/27
Buzarnescu – 25/28

ACES/DOUBLE FAULTS
Williams – 5/2
Buzarnescu – 0/7

BREAK POINTS WON
Williams – 5/14
Buzarnescu – 2/7