Yaz of 1967 and Mays of 1962 were the top 2 guys in my ranking of "indispensable seasons." See Indispensable Seasons Go To WAR! (Or Did Willie Mays Have The Greatest Season Since 1950 in 1962?)
Suppose a team comes in 1st place, finishing 1 game ahead of the 2nd place team. John Smith had a WAR (wins above a replacement player) of 6. Then is "INDWAR" would be 5 or 6 - 1. His team needed 5 of his WAR to get them into at least a tie for first.
Yaz had a WAR of 12.2 and the Red Sox finished 1 game ahead of the Twins. So the Red Sox needed 11.2 of that WAR. Mays had 10.6 and the Giants tied the Dodgers for first place. So the Giants needed 10.6 of Mays' WAR. Mays hit better in any kind of clutch situation you can name that year than he did overall.
The table below shows how he it in certain clutch situations in Sept/Oct of 1962. It also includes his season stats.
Close and Late
Runners in Scoring Position
Runners on Base
Mays did not hit like this in the clutch for his whole career. It looks like he about the same in the clutch for his career as he did overall. Click here to see his career splits at Baseball Reference