The South African world number two celebrated his 35th birthday by pocketing a cheque for 1.0 million pounds ($1.8 million) after clinching his third successive victory in the tournament.
The two players were locked together at the halfway point of the final but Els moved two ahead with an eagle at the 22nd hole and played solid golf to keep Westwood, ranked 37 places below him, at bay.
The British Ryder Cup player, who had inflicted two of Els's four defeats at the World Match Play event, did pull a hole back with a delightful iron shot to birdie the 33rd but Els immediately restored his two-hole cushion.
Westwood, former European number one and Match Play Champion in 2000, made a courageous birdie on the 35th hole but Els sank a snaking 20-foot putt to match his opponent and claim the 52nd title of his professional career.
The South African, who owns a house on the Wentworth estate, also clinched his second successive European order of merit crown. He has now won 22 of his 26 matches in the tournament.
South African Gary Player and Spain's Seve Ballesteros won the Match Play title five times each.
