AP photo by Alastair Grant / Dustin Johnson, left, and Phil Mickelson greet each other on the first tee at the Centurion Club during the first round of the inaugural LIV Golf Invitational Thursday near London.

American stars Dustin Johnson and Phil Mickelson launched tee shots Thursday in LIV Golf's debut tournament near London.

It wasn't long before the PGA Tour said its players who took part in the Saudi-funded league were no longer welcome — even if they already had resigned. Jay Monahan, the PGA Tour's commissioner, held a hard line on his pledge that players could choose one tour or the other, but not both.

Those who had resigned from the PGA Tour — Northern Ireland's Graeme McDowell said he did so 30 minutes before he teed off — were no longer eligible on any of its circuits. Those who remained members, such as Mickelson, were suspended.

"These players have made their choice or their own financial-based reasons," Monahan said in a memo to his membership. "But they can't demand the same PGA Tour membership benefits, considerations, opportunities and platform as you."

England's Ian Poulter said he would appeal the ruling. McDowell said he wanted to "keep the high moral ground" by resigning to try to keep litigation to a minimum; the 2010 British Open champion thinks suspensions are a healthy way to go about business.

Mickelson had nothing to say except that he didn't want to talk about the PGA Tour in his first tournament in four months, only to confirm he will play all eight of the LIV events, five of which will be in the United States.

When told that people were interested in his situation, the six-time major champion replied: "I'm very flattered so many people are interested."

Still to be determined is whether those players are ever welcome back. For now, Monahan made it clear that the suspensions include the U.S. team for the Presidents Cup, which is sanctioned by the PGA Tour. (The golfers who oppose the Americans in that biennial event — an international team excluding European nations — are determined by the Official World Golf Ranking.)

Monahan said the players who resigned will have their names removed from the PGA Tour standings (FedEx Cup and Presidents Cup) after this week. He said the tour will make sure those who haven't resigned will not affect rankings on various lists of tour players.

The United States Golf Association already has said eligible players can still compete next week in the U.S. Open. The PGA Tour does not run the major championship tournaments, with the R&A overseeing the British Open, the PGA of America running the PGA Championship and Augusta National Golf Club responsible for the Masters.

Justin Thomas, who last month won the PGA Championship for the second time in his career, and four-time major champion Rory McIlroy of Northern Ireland are playing this week at the PGA Tour's Canadian Open. Both welcomed the decision.

"I think anybody that's shocked clearly hasn't been listening to the message that Jay and everybody's been putting out," Thomas said. "They took that risk going into it, whether they thought it was a risk or not. I have great belief and great confidence in the PGA Tour and where we're going and continuing to grow to, and those guys just aren't going to be a part of it."

Ten players have resigned, a list that includes Johnson and Spain's Sergio Garcia, an 11-time winner on the PGA Tour and the 2017 Masters champ. Mickelson, who has lifetime membership with 45 PGA Tour titles, is among those who has not.

some text
AP photo by Alastair Grant / LIV Golf Invitational entrant Scott Vincent, right, speaks to tour leader Greg Norman on the first tee Thursday at the Centurion Club near London.

LIV Golf, run by World Golf Hall of Famer Greg Norman and funded by Saudi Arabia's sovereign wealth fund, responded to the PGA Tour's decision by calling it vindictive and divisive.

"It's troubling that the tour, an organization dedicated to creating opportunities for golfers to play the game, is the entity blocking golfers from playing," a released statement from LIV Golf read. "This certainly is not the last word on this topic. The era of free agency is beginning as we are proud to have a full field of players joining us in London, and beyond."

At issue is players competing without a conflicting event release from the PGA Tour.

Players typically receive three such releases a year for tournaments on other circuits, such as the European-based DP World Tour. Monahan denied releases for LIV Golf because it is an eight-tournament series that plans to compete directly with the PGA Tour in the United States. The tour does not allow releases for events in North America.

"We have followed the tournament regulations from start to finish in responding to those players who have decided to turn their backs on the PGA Tour by willfully violating a regulation," Monahan wrote.

LIV Golf has paid enormous signing fees, with The Daily Telegraph reporting $150 million for Johnson, and Mickelson declining to dispute reports he was paid $200 million. Both are more than Tiger Woods' career earnings on the PGA Tour.

Norman, a 67-year-old Australian, has said LIV would support the players even if it wound up in the courts. McDowell said some players already have spoken to lawyers.

"We haven't been issued releases. We feel like we should have been issued releases. We've done it for the last 20 years, operated all over the world," McDowell said. "Listen, we all know the situation is about something bigger. It's competition and it's not liked. They are having to play the game the way they feel they have to play it, which is playing hard ball."

The DP World Tour has not said whether it would suspend its players. It has an alliance with the PGA Tour commercially, including the first co-sanctioned events this year on both sides of the Atlantic Ocean.

The first test for PGA Tour players figures to be the Travelers Championship, the week after the U.S. Open. Johnson was among those listed in the field.

Thursday's LIV Golf Invitational was being streamed on YouTube and Facebook. Before the opening round at the Centurion Club, Norman said he was thrilled to see an effort 30 years in the making come to fruition.

The two-time British Open champion tried to start a World Golf Tour in the 1990s for only the elite players and had a TV contract lined up until the PGA Tour quashed the moment with support from Arnold Palmer. That circuit never got off the ground.

This one did, with the backing of riches the likes of which golf has never seen.

Each tournament offers $25 million in prize money, with $4 million for the individual winner. The PGA Tour's richest event is The Players Championship at $20 million. This week's Canadian Open, which has five of the top 10 players in the world, has an $8.7 million purse.

At LIV's debut event, attendance was sparse and there were no signs of the Saudi backing across the Centurion Club, nor any sponsor branding.

Mickelson was sporting a black cap adorned by his personal logo featuring a silhouette of himself playing golf, replacing the KPMG-branded one that was worn before the corporate sponsors dropped the deal in February after he disparaged the PGA Tour and Saudi Arabia. He matched Johnson with a 1-under-par 69.

Charl Schwartzel, the 2011 Masters champion, opened with a 65 for a one-stroke lead over fellow South African Hennie du Plessis. Scott Vincent of Zimbabwe and Phachara Khongwatmai of Thailand each shot a 67.

LIV is running curtailed 54-hole, three-day tournaments, with a shotgun start in which players all tee off on different holes. In addition, the field is split into 12 teams and the top three will share $5 million on top of the $20 million prize fund per event shared between the golfers individually.