Normally, relief outings last only a few innings with one exception: When a long man is brought in. In that case, a starting pitcher that didn’t make the rotation, is sent to the mound because the actual starter’s stuff isn’t working. 114 years ago, something similar happened with a notable feat that the game ended to be a no-hitter and the outing was perfect.
We are talking June 23, 1917: A game between the Boston Red Sox and the Washington Senators. Babe Ruth, who started the game and walked the first batter, didn’t agree with the call and punched the home plate umpire in the face, resulting into an ejection.
The Red Sox sent Ernie Shore to the mound. A wise decision. The one runner that was awarded a walk, was thrown out at a stealing attempt. From the first batter he faced, Shore recorded out after out after out. Eventually, he retired all 26 batters he faced.

So you may say that the 8.2 innings that Shore was on the mound, were the longest and best relief outing ever. For sure it was a combined no-hitter, as Ruth walked the only batter he faced.
Shore had four winning seasons with the Red Sox but enlisted in the military in 1918. After his return, he joined the Yankees, as Red Sox owner Harry Frazee had sold his contract, which did with many of his players. Shore wasn’t as successful with the Yankees as he was with the Red Sox. After two seasons, he was released and he played one more season in the Pacific Coast League.