Johnson had teed-up at TPC Sawgrass under threat from those ranked No. 2 to No. 5 in the world and it was the second-ranked Thomas who finally attained the summit.
And then there are the thoroughbreds slightly further back like McIlroy and Jason Day, both former World No 1s, who are eminently capable of putting a hot streak together in a run of big tournaments and wrestling back top spot. Jon Rahm, Jordan Spieth and Justin Rose also could have dethroned Johnson during the Players Championship. Thomas finished seven shots back in a tie for 11 at 11-under-par 277 after carding a 6-under final round on Sunday.
With the result, the US PGA Championship victor was confirmed as the new world number one.
Thomas held the No. 22 spot in the world ranking at the end of 2016.
Johnson finished tied for 17 at the Players Championship at 10 under, but Thomas' one stroke advantage was just enough to earn the ranking.
For a start Spieth, who is back up to No 3 in the rankings, is in action this week in his native Texas at the Byron Nelson Invitational desperate to put on a show for his home fans.
Thomas has won eight times on the PGA Tour including one major which came at the 2017 USPGA Championship at Quail Hollow. He won $9,921,560 plus a $10 million bonus as the FedEx Cup champion a year ago.
During his career at Alabama (2011-13), Thomas helped lead the Tide to the 2013 NCAA National Championship - the first in program history.