Musgrove, who caddied for Seve Ballesteros when the Spaniard won the Open in 1979, took hold of Lyle and simply told him: "Just remember how well you're playing."
Lyle, who had started the day at six under par, reached the turn in 34, was eight under for the tournament, and was leading the field by three strokes. At the 11th he left his chip shot short and two-putted from 10ft for a bogey five.
At the 12th, one of the most difficult par-threes in the world, he hit the ball with the bottom of his eight-iron. The direction was perfect, the length was not. It landed on the front bank and rolled inevitably into the water. Lyle held his head in his hands. He had to drop, under penalty, from in front of the lake and was left with a devillish chip shot. He did well to salvage a double-bogey five.
The obituary writers were sharpening their pencils. Perhaps the Lyle of old would have succumbed. Instead, he gritted his teeth and unleashed a massive drive down the 13th. The Masters, as they say in Augusta, is not over until it's over.
"After leading for so long I was determined not to throw it away," said Lyle. "I wasn't interested in being second."
Mark Calcavecchia, playing the hole in front, had gone through Amen Corner in 3-3-4 compared to Lyle's 5-5-5.
For the first time in 40 holes Lyle had lost the lead, but he had not lost his nerve. Suddenly the strain of being out in front was lifted from his shoulders. Calcavecchia, a 27-year-old US Ryder Cup player from North Palm Beach in Florida, could see himself being measured for the green jacket.
At the 15th, 16th and 17th Calcavecchia made three tricky putts to save par. He finished with a 70 for an aggregate of 282, two under for the day and six under for the tournament. At the 15th Lyle came within a whisker of an eagle three when his chip lipped out and rolled five feet past.
He missed the return putt, had to settle for a par five and was left with the extraordinarily difficult task of making two birdies in the final three holes to win. That he did so underlines the maturity and character of a 30-year-old at the height of his mental and physical powers.
At the par-three 16th he holed a 15ft downhill putt which had a 2ft borrow. If it had missed, it would have gone 6ft past. The 18th is a par four of 405 yards; not since Arnold Palmer in 1960 had a golfer made a birdie on the final hole to win the tournament.
Lyle, as he had all week, hit a one-iron off the tee and for the second time he held his head in his hands. The ball found the front-left fairway bunker. Lyle feared the worst. "It has a steep face and it was the last place I wanted to be. I didn't think I could get on to the green from there. The lie was better than I thought and the ball was about 3ft from the lip of the bunker."
Even so, the height of his ambition from there was to get a par four and force a play-off. He had 150 yards to go and he picked the ball out of the bunker sweetly and cleanly. After making the swing he leapt out of the bunker to follow the flight path, strong evidence that he liked the shot.
It landed perhaps 30ft past the pin, appeared to come to a stop and then rolled downhill to finish 10ft from the hole. "I will," said Lyle, "remember that shot for the rest of my life."