Pierce scored 27 points - his best performance of this year's finals - and the Celtics withstood 38 points from Kobe Bryant to beat the Los Angeles Lakers 92-86 on Sunday night and take a 3-2 lead in the best-of-seven series.
Game 6 is Tuesday night in Los Angeles, and a victory then or in Game 7 in L.A. on Thursday would give the Celtics a record 18th NBA championship.
Pierce was the finals MVP in '08, when the new Big Three beat the Lakers to raise an NBA-record 17th banner to the rafters at Boston's TD Garden. Bryant was the finals MVP last year, when the Lakers beat the Orlando Magic to win their 15th championship.
The Associated Press contributed to this report.