Australian Gavin Coles fired an impressive four-under-par final round, but it was not enough to halt American Zach Johnson&aposs charge to victory at the AT&T Classic tournament. US Masters champion Johnson kept his cool to defeat Japan&aposs Ryuji Imada in a sudden-death play-off in Georgia. The 31-year-old birdied the first extra hole – the 18th – to take the title after third-round leader Imada found the water. A storming final round 67 from Johnson looked to have sealed his third title, but a birdie from Imada at the last forced a play-off. Johnson&aposs chance for victory came when Imada fired his second shot of the play-off at the par-five 18th into the drink at the front of the green. “I admire (Imada&aposs) courage in going for the shot,” said Johnson. “I understand why he hit his shot. If it was a little bit right it may have carried on.” “We (then) thought about laying up, but at the same time I had a perfect lie, perfect yardage. It was a really pretty routine shot.” Imada&aposs failure denied him a maiden PGA Tour victory, but insisted he had no regrets over the shot which landed in the water. “I&aposm obviously disappointed right now but I think the decision I made on the play-off hole was the right one for me,” Imada said. Coles (68) made three birdies and a stunning eagle at the par four 17th to finish with his third under-par round after a disappointing opening round of 74. Compatriot Steve Elkington (73) was a shot behind Coles while Mark Hensby (74) was a further nine strokes off the pace.