Boston led the entire game against the Miami Heat, with a maximum of 17 points.
Although Miami managed to barely make it into the final minutes.
The final score was 100-96 to Boston.
The match's best scorer was Miami's Jimmy Butler with the number 35 in the points record.
Boston's Al Horford took the most returns - 14.
The Boston Celtics now have a chance to become the NBA's most champion team.
The club already has 17 titles - the first came in 1957 - but so do the Los Angeles Lakers, although five of them came in the 1940s and 1950s when the club was based in Minneapolis.
The final series between Boston and Golden State begins the night before Friday, Swedish time.
The Warriors then had to rest for a week because it only took five games for them to beat the Dallas Mavericks in the Western Conference semifinal series.
The final, like all other matches in the playoffs, is decided in the best of seven.
The clubs have met in the final once before - in 1964 when the Warriors had led San Francisco.
That time, Boston won 4-1 in matches.