I'm struck that no one has yet to mention Irwin at the 1979 US Open (75 final round), Seve at the Masters in 1980 (72 final round, the worst among the contenders that year), and Lehman's final-round 73 at Lytham in 1996, easily the worst round among those contending for the title that year. Of course, all of those golfers went on to win those championships, despite their mediocre play in the final day, so they never got the label of throwing away a tournament at the end.
Els didn't shoot one round over par this year at Lytham -- the only golfer in the field who can claim that accomplishment. When the rest of the contenders were throwing up 73s, 74s and 75s, he shot a solid 68 and closed with a birdie on a tough hole.
Rich -- I'm not sure I'd characterize Faldo as clearly backing into either of his two Muirfield wins in the Open. He famously ground out 18 straight pars in 1987, and was within one of the lead after both 36 and 54 holes. Folks remember Zinger's bogey on 18, but Faldo was there to take advantage and had a solid day of golf in tough conditions. He was running away with the tournament in '92, with a four-stroke lead entering the final round, and after indifferent play around the front nine, came back with late-round birdies to edge Cook, who admittedly did bogey the last. But Cook didn't just hand the tournament to Faldo.