I'm sure it's 1, but I can't think of any particular instances of that.
One strange instance that sticks out in my mind was during the 2011 World Series, when Tony LaRussa made a pitching change and called Lance Lynn in from the bullpen. Lynn faced one batter, intentionally walked him, and then another pitching change was made.
If you're talking about complete games by starting pitchers, Charley "Red" Barrett of the Boston Braves only needed 58 pitches to go all 9 innings on August 10, 1944.
Red Barrett Fifty-Eight Pitch Complete Game | August 10, 1944 at Crosley Field
On many occasions, a relief pitcher has come into the game, then been substituted without ever throwing even one pitch, so the answer to the question as worded is 0. The fewest pitches in a Major League game by a pitcher who pitched a complete game is 44, accomplished by Charlie Barrett.
No pitcher in baseball history has ever thrown the minimum of 27 pitches in a 9 inning game.
Fewest losses ever? Or fewest losses in a season?
In 1944, Charley "Red" Barrett of the Boston Braves threw only FIFTY-EIGHT pitches during a nine inning complete game. Barrett's Braves shutout the Reds 2 - 0 and the game set major league records for least number of pitches known to have been thrown by a single pitcher in a complete game and shortest game played at night.
On 1944 August 10, Red Barrett of the Boston Braves needed on 58 pitches to shut out the Cincinnati Reds 2-0.
The fastest baseball pitcher is Aroldis Chapman. He pitched the fastest fastball ever recorded, clocking at 105 mile per hour.
No one with that exact spelling has ever played Major League baseball.
Satchel paige more than 105 mph
no yet but there is one in college 2008
Satchel Paige was the fastest pitcher ever witnessed
In Major league baseball, there has never been a pitcher who recorded 5 strikeouts in an inning as of August 13th 2012.