The World Number Four, trying to follow Sergio Garcia and Henrik Stenson, goes into the final round of The Players Championship at Sawgrass in Florida one ahead of Australian Robert Allenby.
That was the advantage he held at halfway, but it was far from smooth sailing for the Worksop 37 year old before he handed in a two under par 70.
First American Heath Slocum moved into a two shot lead before bogeying the 13th and 15th and horribly dumping his tee shot into the water at the near-island green short 17th.
Just before that Allenby had made it a three-way tie thanks to a 14 foot eagle putt at the long 16th and a 12 footer on the dangerous next.
But Westwood - third, third and second in the last three Major Championships - kept his cool and with a birdie at the 523 yard 16th and two closing pars he posted a 14 under aggregate.
Allenby was round in 67 to take over as closest challenger, while one further back are Italian Francesco Molinari and two more Americans in Ben Crane and US Open Champion Lucas Glover.
But there is still a chance that Phil Mickelson will deny Westwood just as he did at The Masters Tournament a month ago - and that the left-hander will take the World Number One spot after 244 weeks at second.
Mickelson moved into joint 11th with a 66 and is five behind - just as Stenson was before charging through to win by four 12 months ago.
To go top of the rankings for the first time in his life Mickelson has to win and Tiger Woods has to be outside the top five.