Naomi Osaka's clay-court season started with a loss in the first round of the WTA Madrid Open against Lucia Bronzetti on Tuesday.

Japan's four-time Grand Slam champion stumbled on match point as Bronzetti completed a 6-4, 2-6, 6-4 win before checking Osaka was fine as they approached the net for a post-match handshake.

55th-ranked Osaka was unseeded in Madrid for her first match in almost a month since reaching the fourth round of the Miami Open. Italy's Bronzetti will play fifth-seeded American Madison Keys in the second round. She will be seeking her third third-round appearance at a WTA 1000 event.

Meanwhile, Alexandra Eala finds herself in a rematch with Iga Swiatek in the second round in Madrid after stunning the Polish player as a wild card in Miami last month. 19-year-old Eala won her first-round match 6-3, 6-2 against Viktoriya Tomova.