How many minutes of playing time did the longest professional tennis match — Isner vs. Mahut at Wimbledon 2010 — last?

Answer

665 minutes

The match ran 11 hours 5 minutes across three days, with the final set alone finishing 70-68 and lasting longer than any other complete match in history. Wimbledon later put a plaque on Court 18 and eventually introduced final-set tiebreaks partly because of it.

Source: Guinness World Records / Wimbledon (AELTC)