At six hours and 35 minutes, it was the longest match ever played on Centre Court and the second-longest match at The All England Club.
The game dragged on for a total of six hours and 36 minutes, with the final set alone taking two hours and 54 minutes.
The South African won the opening set on a tie-break but lost two subsequent tie-breaks before he levelled the match 6-4 in the fourth.
It was the second-longest match in Wimbledon history and longest one-day match in Wimbledon history.
Anderson, who also won a marathon game against Roger Federer in the quarter-final, will face the either Novak Djokovic and Rafael Nadal in Sunday's final, both of whom sat in the locker room for the duration of the first final.
But it falls short of the 11 hours and five minutes that it took for Isner to beat France's Nicolas Mahut 70-68 in the fifth set in their first-round match at Wimbledon in 2010.
Each player held his next serve before Anderson broke Isner again to go up 5-4 and then proceeded to serve out the set to send the match to a decisive fifth set.
The 33-year-old American´s composure wasn´t helped by a delay caused by a ball boy slipping and falling. Isner in particularly started to appear tired at the set wore on.
"With how I'm feeling physically and mentally, I'm in a very good spot", Isner said in his post-match press conference.
On the most crucial point of the match, Anderson recovered after a fall and hit a lefty forehand to go up 0-30 while Isner was serving at 24-24.
Nadal, 32, is back in the semi-finals at Wimbledon for the first time since 2011 when he finished runner-up to Djokovic.
It will be the second Grand Slam final for Anderson, who reached the final of the US Open a year ago to Rafael Nadal.
"I feel confident in sort of baseline exchanges I'd say quite a lot with John".