Golf will likely look a little different when it's included at the Olympics for the first time in more than 100 years at the 2016 Rio de Janeiro Games, but not like this.
"Courses usually don't move this much, but it's definitely going to be fun," Garcia said of the stunt Monday under London's historic Tower Bridge.
So will golf at the next Olympics.
"It would be really cool to be part of the opening ceremony," Johnson said. "Really cool."
Garcia pitched three out of five shots onto the artificial green with a lob wedge from about 75 yards. Johnson nailed two, or maybe it was three.
Even the players weren't sure where some of the purple balls — the colour of the London Olympics — ended up.
"I thought you were going to make it soft," Johnson said as practice shots bounced off the bright green turf and into the river.
Behind the floating green, curious Londoners peered over the edge of the famous bridge in bright evening sunshine to see what was going on.
There was even a long-jump style slow clap for the players as they took their shots. Nothing like the silence when golfers tee off at Augusta National, or any other top course.
While organizers haven't yet settled on the format for golf in 2016 — maybe stroke play, maybe match play — both players were excited for its inclusion.
"I think it's going to be very special if I can represent my country," said Johnson, who is from the U.S. "Being an Olympian is more about being an athlete and being part of something more than just you."
Garcia, who is from Spain, remembered the 1992 Barcelona Olympics as his favourite games. No surprise.
He also remembered the Spanish football team's late win in the gold-medal match that year.
Johnson was all about the U.S. "Dream Team" in Barcelona.
"Those moments stick," Garcia said. "After these Olympics go by it will be the one we're in and everyone will be talking about it."
Golf, like tennis, will get top players more used to playing for themselves into the Olympic spirit when it returns for the first time since 1904 in Rio. And while Garcia and Johnson agreed a major title was still the ultimate prize in their sport, the Olympics was something unique for a golfer.
Garcia said he would take a silver medal over second place at a major any day. Johnson wasn't sure what he'd prefer: an Olympic gold medal or a win at a top non-major like the Players Championship.
"I don't know, that's a tough one," he said.
The pair also expressed sympathy for Adam Scott after the Australian's late collapse at the British Open on Sunday.
Garcia and Johnson have both experienced agonizing slumps at majors while in position to win.
"Unfortunately, I've been in a similar situation and I really feel for him. You've got to look at the positives," said Garcia, who sent Scott a text message to show his support. "Unfortunately, this game is a game of inches."