The Celtics finished the regular season with a league-high 66-16 record, the most victories in a single season since their last championship season in 1986. Their record ensured them home court advantage throughout the playoffs. The previous year's champion Los Angeles Lakers lost to the Celtics in six games in the first round of the playoffs.
The 1966-67 NBA season was the first season that the playoffs were 16 teams divided into four groups: A, B, C, and D. The top two teams from each group advanced to the Eastern and Western Conferences, respectively. The winners of these conferences met in the Finals. The other eight teams were eliminated from playoff contention.
In addition to winning the regular season title, the Celtics also won 17 games in a row at one point during the season. This is the longest current streak in the NBA. The team's overall dominance can be seen by the fact that they had more wins than any other team in the NBA during this season.
They also have the highest winning percentage (.769) of any non-defending champion in NBA history. The previous year's champion Lakers fell to the Celtics in six games in the first round of the playoffs.
The Boston Celtics were defeated, 140-116, by the Philadelphia Sixers in Game 5 of the Eastern Division playoffs on April 11, 1967, after winning the previous eight straight NBA titles. So the Celtics' reign came to an end, but only momentarily. Boston went on to win the next two seasons, giving the Celtics a total of ten championships in 11 seasons. During that period, they also lost only one game.
In 1966-67, the Celtics finished first in the Eastern Conference with a 52-20 record, but they had to go through the Pistons, who had a 48-19 record, in the first round. The series was tied 2-2 before Boston won the next three games to advance to the finals. In the championship series, the Celtics faced Jerry West's Lakers, who had beaten them in five games in the previous season's finals. This time, however, the Lakers were no match for Boston: The Celtics swept them 4-0 to claim their eleventh title.
Following their tenth championship, the Celtics declined slightly, finishing second in 1968-69 with a 44-38 record. They then dropped to third place in 1969-70, behind a resurgent Lakers team that captured their fifth title. The Celtics bounced back from that disappointment by winning their twelfth and final championship in 1970-71, when they defeated Los Angeles in seven games. Following that victory, coach Red Auerbach retired from coaching, ending what had been a long career in Boston.
From 1957 until 1969, the Celtics were one of the most successful sports clubs in history, winning 11 of 13 National Basketball Association (NBA) titles. They have won 17 NBA championships in all. The Cs also won six American Football League (AFL) championships in 1967, 1968, 1969, 1970, 1971, and 1972, making them the only team to win championships in three different professional basketball leagues.
In addition to their success in the NBA and AFL, the Celtics also won the first two World Club Championship tournaments in 1957 and 1958. By contrast, the current Boston Bruins hockey team has never won a major professional trophy - the Stanley Cup - having last appeared in 1971-72. The Bruins are currently working on their third trip to the NHL playoffs in four years.
The Celtics' dominance on the court made them popular among fans, who voted them as the top team in the NBA during each season from 1957 to 1969 except for 1962 when the Lakers ranked higher. However, after losing several games in the 1969 season, the fans turned against the club, voting them out of first place that year. Although the Celtics still managed to win the championship that year, they did not enjoy the same popularity anymore. The franchise has never been back to the top since then; instead, it has finished in second place or below every year since then.