March 5 (Reuters) - Dustin Johnson surrendered a big lead before cementing his world number one ranking with a one-stroke victory at the WGC-Mexico Championship in Mexico City on Sunday.
American Johnson built a four-stroke advantage on the back nine before giving it all up to young Spaniard Jon Rahm at Club de Golf Chapultepec.
But Johnson, after back-to-back bogeys, avoided any further dropped shots in a three-under-par 68, tapping in at the last from a few inches.
He finished at 14-under 270 for his second consecutive victory, after winning at Riviera in California two weeks ago.
Englishman Tommy Fleetwood (66) birdied the last to claim second place on 13-under, while Rahm faded late to tie for third with Englishman Ross Fisher on 12-under.
Overnight leader Justin Thomas faltered with a 72 to finish three strokes behind, equal fifth.
Johnson has now won 14 times on the PGA Tour, including four victories in World Golf Championships events. (Reporting by Andrew Both in Cary, North Carolina; Editing by Toby Davis)