Woosnam, 44, is attempting to become the oldest champion in the 38-year history of the event.
Harrington, 14 years Woosnam's junior, ended the dream of Sam Torrance when he ground down the European Ryder Cup captain for an eventual 4 & 3 victory.
Torrance, 48, was 2-up through 16 holes, but lost two of the last three holes in the morning round and then dropped four of the first five in the afternoon.
"That's nine holes less than I expected to play," Woosnam said. "I think it's important to conserve energy and I was pleased getting the match over so quickly."
I might have expected to play. I think it's important to conserve energy and I was pleased getting the match over so quickly."
Woosnam shot a 66 in the morning and went to lunch with a 7-up advantage. The Welshman is trying to win the event for the third time.
"I was brought up to take it on the chin and accept defeat gracefully," Westwood said. "I just played like an idiot and he played great. There is nothing else I could do."