It wasn't pretty, but McIlroy's 4-under 67 on Labor Day at TPC Boston was enough to hold off Oosthuizen, who shot even par in the final round after starting the day with a 3-stroke lead.
With three wins, the 23-year-old Northern Irishman now equals Tiger Woods for the most tour wins this season. Woods might still have a chance to get his 11th player of the year award if he wins the two remaining playoff events, but McIlroy's impressive 8-shot win at the PGA Championship is hard to surmount for style points or quality of victory.
"Three is a great number," McIlroy said. "I'd like to make it four or five. I'm very pleased at how hard I worked on my game leading up to these few weeks, because I felt like it was nearly there and I just needed to stay patient.
"I felt like I turned a corner at Akron [at the WGC-Bridgestone], and then it really clicked at Kiawah [at the PGA Championship] and I've just kept it going from there."
In front of a colorful Boston crowd, McIlroy continued to show a poise and grace that belies his 23 years and reiterated why he is not only the best player in the world, but also the player to beat for at least the next decade.
The most impressive thing about McIlroy's win on Monday was that he did it mostly without his A-game. While he did have four rounds in the 60s (65-65-67-67), he wasn't the same player who won the PGA Championship by 8 shots or the one who took the U.S. Open by the same margin last year at Congressional.
After a front-nine 4-under 32, McIlroy went even par on the inward side. At the reachable par-5 7th hole, he left his approach shot 50 yards short of the green with a chunky iron shot. He needed a 5-foot bogey putt at the 17th to keep a 1-shot lead over Oosthuizen after hitting a couple of very poor shots. Then, at the easy par-5 18th, a par was good enough to fend off a playoff when Oosthuizen missed his 14-footer for birdie.
"I think the good start set me up for a solid back nine," McIlroy said. "There [were] a couple of shots on the back nine I won't take back now, but if I could have them, I would have."
What's left for McIlroy to do now is win the playoffs and lead the European Ryder Cup team to its fifth win in the past six matches. Come the start of the biennial matches at the end of September at Medinah, it will be more than symbolic that McIlroy is the best player in the world. Playing in front of a partisan U.S. crowd, there will be a mark on his head.
Woods will be the marked man on the other side for the Americans in the Ryder Cup matches. No matter who was ranked No .1 in the world, Woods was always the best player in his seven previous matches.
Right now, Tiger couldn't beat McIlroy in a head-to-head duel, either in a Sunday singles match at the Ryder Cup or in the final round of a FedEx Cup playoff event or in a major. McIlroy is too consistent with his driver and putter for the erratic 14-time major champion.
McIlroy is no longer the man in waiting. Get used to always hearing McIlroy's name in conjunction with Tiger's. They are the best rivalry in golf.
At the Deutsche Bank, Woods finished third after shooting a 5-under 66 on Sunday. Playing with Dustin Johnson in the group ahead of McIlroy and Oosthuizen, Tiger never really mounted any serious pressure on McIlroy and Oosthuizen after beginning the day 6 shots back of the lead.
Yet with his $544,000 third-place check, Tiger went over $100 million in career PGA Tour earnings. The week also marked the first time since the 2009 BMW Championship that Woods had four rounds in the 60s in a PGA Tour event.
"After the first day, we figured it was going to be pretty low," Woods said. "I wanted to get to 20. I figured if I got to 20 with one hole to go, give myself an option to go 21 or 22, I thought that might have a chance."
Perhaps that's the Tiger of the future, a man always coming up a little short in a race to catch McIlroy. We're not talking about McIlroy supplanting Woods as the best of all time. It will be hard for anyone ever to equal Tiger's career achievements, but McIlroy has come fully on the scene to stop the proliferation of more Tiger records.
Woods might get his first comeback player of the year at the end of the season, but the 11th player of the year honor that was once in his grasp will go to McIlroy.
The kid from Holywood, Northern Ireland, has earned it.