John Spencer, who won the title at his first attempt in 1969 and again in Australia during 1970, came to the Crucible ranked only eighth and therefore occupying the last seeding position.
Spencer was in good form
He had been off form and was using a two-piece cue, which he had had for only two months.
The championship, the first to be played at Sheffield's Crucible, a small theatre-in-the-round suggested as a snooker venue by Carol Watterson, the wife of promoter Mike Watterson.
But Spencer, who trailed John Virgo by three frames on two occasions, before beating him 13-9 in the first round, improved as the championship progressed.
In the last eight, he defeated Ray Reardon, five times world champion between 1970 and 1976, 13-6.
In the last four he obtained a snooker to prevent John Pulman taking the match the distance as he prevailed 18-16.
Cliff Thorburn had beaten durable Australian Eddie Charlton 13-12 in the quarter-finals and Dennis Taylor 18-16 in the semis and constructed a healthy 15-11 lead in the final.
Spencer, though, raised his game once more to draw level at 15-15 and from 22-21 claimed the next three frames to win his third world title.