Former world number ones Venus Williams and Kim Clijsters made triumphant returns to the WTA after long layoffs with victories on Wednesday at the WTA and ATP Miami hardcourt tournament.
Seven-time Grand Slam champion Venus Williams, who has not played a WTA event since pulling out of last year's US Open, defeated Japan's comeback queen Kimiko Date-Krumm 6-0, 6-3 in 77 minutes.
Williams announced at last year's US Open that she had been diagnosed with the auto-immune disorder Sjogren Syndrome.
The illness saps her energy and causes pain in her joints.
Federer to skip Monte Carlo masters
World number one Novak Djokovic and seven-time consecutive title holder Rafael Nadal will head the field for the April 15-22 Masters 1000 in Monte Carlo, but Roger Federer will be missing.
"We're keeping a wild card to one side for Roger," tournament organiser Zeljko Franulovic said of the Swiss world number three.
"You never know, even if he has played a lot since the start of the season. He's decided in the past to come at the last minute."
Should Federer be absent, the six other players in the top seven are expected to be there.