Using Basketball Reference's Player Game Finder with the following search criteria:
In a single game, from 1964 to 2019, in the playoffs, round is Finals, team lost game, sorted by descending Points
The top 5 scoring performances in the NBA finals that resulted in a loss are:
1) LeBron James - 51 points, Game 1, 2018 NBA Finals (Cavaliers at Warriors)
2) Stephen Curry - 47 points, Game 3, 2019 NBA Finals (Raptors at Warriors)
T3) Jerry West - 45 points, Game 4, 1966 NBA Finals (Celtics at Lakers)
T3) Jerry West - 45 points, Game 2, 1965 NBA Finals (Lakers at Celtics)
T5) LeBron James - 44 points, Game 1, 2015 NBA Finals (Cavaliers at Warriors)
T5) Shaquille O'Neal - 44 points, Game 1, 2001 NBA Finals (76ers at Lakers)
T5) Michael Jordan - 44 points, Game 3, 1993 NBA Finals (Suns at Bulls)
T5) Rick Barry - 44 points, Game 6, 1967 NBA Finals (76ers at Warriors)