Vasek Pospisil launched a stunning tirade during his three-set defeat to American qualifier Mackenzie McDonald in the first round of the Miami Open on Wednesday.

The Canadian former world number 25 was docked a point for verbal abuse, subsequently conceding the first set, before a meltdown during the change of ends.

Pospisil used a profanity in reference to ATP chairman Andrea Gaudenzi when speaking to chair umpire Arnaud Gabas.

“[Gaudenzi was] screaming at me in a player meeting for trying to unite the players — for an hour and a half," Pospisil said to Gabas. "If you want to default me, I’ll gladly sue this whole organisation.”

He did fight back to win the second set but ultimately lost to McDonald 6-3 4-6 6-3.

Pospisil, who is nowadays ranked 67th, was joined among the first-round exits by last week's Mexican Open semi-finalist Dominik Koepfer, who went down 6-1 6-4 to wildcard Hugo Gaston as he claimed his first career Masters 1000 win.

Sam Querrey, ranked 63rd, also bowed out 6-3 6-4 to Lu Yen-hsun, who will meet world number two Daniil Medvedev in the second round.

YOUNGSTER BEATS VETERAN

Australian youngster Alexei Popyrin secured his maiden win at the Miami Open, knocking out the oldest player in the draw Feliciano Lopez 6-4 7-6 (7-4).

Popyrin, 21, claimed his first ATP Tour title last month in Singapore and backed that up with a strong display against the 39-year-old former top 20 Spaniard.

Recent Open 13 Marseille runner-up Pierre-Hugues Herbert got past Portugal's Pedro Sousa 6-1 6-3, while South Africa's Lloyd Harris defeated Emilio Nava 6-4 7-6 (9-7).

Frances Tiafoe won in the final match of Wednesday, coming from behind to beat Stefano Travaglia 5-7 6-4 6-2.

COMEBACK CAM

Brit Cameron Norrie produced a heroic final-set fightback to claim his spot in the second round, where he will face Grigor Dimitrov.

Norrie trailed 5-1 in the third set against Yoshihito Nishioka, before winning 6-1 3-6 7-5, winning the last six games to clinch victory.

The 56th-ranked Brit sent down eight aces in the victory, although he got the edge on return and converted seven of his 10 break points.

SECOND ROUND

Top seed Medvedev will face Lu on Thursday, while third seed Alexander Zverev will take on Finland's Emil Ruusuvuori.

Norrie will meet Dimitrov, while 11th seed Felix Auger-Aliassime faces Herbert and eighth seed David Goffin will take on James Duckworth.

Harris has a match-up against seventh seed Roberto Bautista Agut.