Defending SailGP champion Team Australia capsized its foiling 50-foot catamaran on San Francisco Bay on Thursday, doing major damage to its high-tech wing sail three days before the global league's $1 million, winner-take-all season title race.

The capsize by skipper Tom Slingsby's crew came three days after another title contender, Jimmy Spithill's Team USA, capsized while training off Alcatraz Island. Australia, the season points leader, and the United States have qualified for Sunday's $1 million championship race, the finale of the Mubadala United States Grand Prix. The third finalist will be determined during fleet racing Saturday and Sunday.

The Australian boat — nicknamed The Flying Roo for the yellow kangaroo on the wing sail — pitch-poled, with the right hull digging into the water and carrying the catamaran over onto its side. It came to a rest with its starboard hull and the tip of the wing sail in the water. The port hull was suspended in the air, with some of the crew in the cockpit. The team said there were no injuries.

In a photo provided by SailGP, the Australian team, helmed by Tom Slingsby, capsizes during a practice session for the San Francisco SailGP event Thursday, March 24, 2022, in San Francisco. (Felix DiemerSailGP via AP)

In a photo provided by SailGP, the Australian team, helmed by Tom Slingsby, capsizes during a practice session for the San Francisco SailGP event Thursday, March 24, 2022, in San Francisco. (Felix DiemerSailGP via AP)

Slingsby said the capsize came at the end of a training session, when a gust of wind hit the boat while it was doing a tack bear-away maneuver. He said the crew felt in control and wasn't sure what it did wrong, but called it an unforced error.

“We've done 20 of those maneuvers in the last few days with no issues. It was all going well until it wasn't," Slingsby said. “We're a little unsure but obviously upset that we've done so much damage to the boat.”

The wing sails look and perform like an airplane wing, helping power the F50 cats to close to freeway speeds as they skim above the waves on hydrofoils. Slingsby said several of the wing sail's frames are broken and the flaps “are quite damaged.” He said the shore crew could have some long nights rebuilding the wing.

In this image provided by SailGP, Australia's SailGP Team, helmed by Tom Slingsby, capsizes during a practice session ahead of the San Francisco SailGP in San Francisco, Thursday, March 24, 2022. (Felix DiemerSailGP via AP)

In this image provided by SailGP, Australia's SailGP Team, helmed by Tom Slingsby, capsizes during a practice session ahead of the San Francisco SailGP in San Francisco, Thursday, March 24, 2022. (Felix DiemerSailGP via AP)

Slingsby capsized the U.S. boat during training before the season-opening regatta in Bermuda, when the Aussie boat was still being set up. This is the first time in two seasons he has capsized the Flying Roo.

“It's disappointing. It's not the preparation we wanted and we don't want to create work for anyone," he said. "Unfortunately there's going to be a lot of people having late nights working through the night to try to get us ready. It's not what we want but we know there's amazing people who are going to help us get back on the water.”

Slingsby thinks the Aussies will be OK to race in Saturday's three fleet races. However, he said there could be water damage to various systems that won't be apparent until the boat is racing, so he hopes to be able to practice before Saturday's racing. There will be two more fleet races Sunday before the $1 million finale.

Slingsby is an Olympic gold medalist and was strategist for Spithill when Oracle Team USA staged a sunning rally to win the 2013 America's Cup on San Francisco Bay.

The Aussie skipper beat Team Japan's Nathan Outteridge in for the inaugural season championship in 2019 and the $1 million prize. Outteridge and Team Spain's Phil Robertson have the best chances of clinching the third spot in the podium race.

Follow Bernie Wilson on Twitter at https://twitter.com/berniewilson