Andrew Coltart has described Phil Mickelson's victory at the PGA Championship as the kind of story that is "not supposed to happen".
Mickelson became the oldest major champion in history as he secured his sixth major title at Kiawah Island on Sunday, just three weeks before his 51st birthday.
He will be looking to follow that up with victory in the US Open at Torrey Pines in California next month at a course he knows well, and could also compete in his 13th Ryder Cup later this year.
- Magical Phil Mickelson makes major history with PGA win
- Phil Mickelson has renewed belief for US Open bid
- Tiger Woods: Phil Mickelson's major win 'inspirational'
"It's just incredible. We thought Phil's career had peaked several years ago, he was already starting to focus on the Champions Tour," Coltart told Sky Sports News.
"He has already had a couple of victories on the Champions Tour, which is their [equivalent of] the Seniors Tour over there [in the USA].
"Physically and mentally, we all thought the challenges of contending in a major were past him. Clearly not!
"Mickelson's mental and physical fortitude, as well as his technical ability, stood tall and he came out victorious.
"These kinds of stories are not supposed to happen. The young and the strong are supposed to prevail but that wasn't the case.
"It was the legend that is Phil Mickelson.
"It was an incredible feat that Mickelson managed to accomplish."
Mickelson will look to become only the sixth player to complete the career Grand Slam if he can win next month's US Open at Torrey Pines in his hometown of San Diego.
If he does so, he will follow in the footsteps of Gene Sarazen, Ben Hogan, Gary Player, Jack Nicklaus, and Tiger Woods in completing golf's sweep of major tournaments.
Coltart added: "I have no doubt he can do it. Torrey Pines is in his back yard, he was born and brought up in the San Diego area.
"It's fitting that he got an invite to play there but in typical Mickelson fashion, he's gone out of his way and qualified through sheer merit.
"With the skills he possesses and the familiarity he has around that golf course, there's every possibility he could go all the way."
Mickelson could also be part of the US team for this year's delayed Ryder Cup, something Coltart is convinced is also possible if his playing time over the three days is restricted.
"He has managed to qualify and it's going to be interesting," Coltart said of Mickelson's possible Ryder Cup inclusion.
"He's almost given [US Ryder Cup captain Steve] Stricker a conundrum: you have got a 50-year-old who, despite the fact he's won a major, physically he will not be able to handle the challenges of five days of matchplay golf in the Ryder Cup.
"He's going to have to be used sparingly but he will definitely be there, I am sure."