Barty through to fourth round in Miami

Ashleigh Barty defeated Petra Martic to move into the fourth round of the Miami Open.

The 21st-seeded Barty eased past Croatian Martic 6-4 6-3 and will meet fellow Australian Daria Gavrilova's conqueror Elina Svitolina in the round of 16.

Barty struggled with her first delivery - serving at just 35 per cent - but her superior ground strokes proved decisive during the 72 minute encounter.

The 21-year-old Queenslander will meet Svitolina after the Ukrainian world No.4 bounced back from dropping the first set to overcome Gavrilova 4-6 6-0 6-1.

Svitolina broke Gavrilova's serce on seven occasions and was helped by 47 unforced errors by her opponent in the match which last two hours and six minutes.

Venus Williams overcame three match points before rallying past Kiki Bertens 5-7 6-3 7-5.

Williams blew a 5-0 lead in the first set and was down 5-3 in the third set but she swept the final four games, holding serve at love for the victory.

When Williams slammed a forehand winner on the last point, she spun with a grin in celebration, her fist leading the way.

"I'm not sure," eighth-seeded Williams said in an on-court interview when asked how she had pulled off the victory in a match that had 15 breaks of serve.

"I had a lot of chances; she had a lot of chances.

"It didn't look good sometimes but that's why you keep playing to the last point and why I love this game."

Williams, a three-time champion, will next face Johanna Konta, the defending champion.

The Brit advanced with much less drama, beating 22nd-seeded Elise Mertens 6-2 6-1.

Reigning French Open champion Jelena Ostapenko defeated Beatriz Haddad Maia 6-2 7-6 (7-2), Puerto Rico's Monica Puig beat Maria Sakkari of Greece 6-3 7-5 while Danielle Rose Collins saw off Donna Vekic 4-6 6-2 6-1.