The 15th hole is traditionally Tiger's best hole at Augusta, and he appeared to be heading towards an easy birdie that would have given him the outright lead. Instead, the ball hit the flagstick on the fly and the spin on the ball caused it to roll into the water.
Commentator David Feherty summed up the shot perfectly when he shouted "royally cheated!" as the ball raced towards its watery grave.
Tiger went on to bogey the hole and is now one back. Here's the video (via ESPN)...