THERE IS ALWAYS a possibility that either Boston or Washington will upset the Cleveland Cavaliers in the Eastern Conference Finals, or that the Golden State Warriors won't continue to run through the Western Conference playoffs.

Still, if you look at the way the NBA playoffs have progressed so far, there is a high probability that the Cavaliers and Warriors will make history by becoming the first teams to play against each other in three consecutive finals.

There have been 12 other opportunities for it to have happened.

The Boston Celtics and St. Louis Hawks played for the NBA title four times in five seasons between 1957 and 1961, but the Minneapolis Lakers played the Celtics for the championship in 1959.

The Los Angeles Lakers and Celtics have played in consecutive Finals on four different occasions.

The Sixers played the Lakers in the Finals in 1982 and 1983. The Lakers won 4-2 in '82 but the Sixers responded with a four-game sweep the next season.

The New York Knicks lost in 1952 and '53 to Minneapolis; St. Louis ('60 and '61 to Boston); Lakers ('62 and '63 to Boston); Lakers ('65 and '66 to Boston); Lakers ('68 and '69 to Boston); and Utah Jazz ('97 and '98 to Chicago) are the teams that lost both Finals.

On Sunday, Cleveland advanced to its third straight East Finals by sweeping the Toronto Raptors out of the second round.

Whatever issues the Cavs may have had during a regular season that saw them finish with just the second best record in the East, they seemed to have worked them out during the playoffs.

Cleveland is 8-0 through the first two rounds having disposed of the Indiana Pacers and then Toronto.

Talk about being able to turn the switch back on, the Cavaliers finished the regular season by losing four straight games and that cost them the No. 1 seed that went to Boston.

LeBron James has been spectacular for Cleveland, averaging 34.4 points, 9.0 rebounds, 7.1 assists, 2.1 steals and 1.5 blocks.

Kyrie Irving has struggled with his shooting but is averaging 23.8 points and 5.8 assists in the playoffs.

The Warriors have been impressive in sweeping the Trailblazers and Jazz. Golden State has won seven of its eight playoff games by double figures.

Stephen Curry and Kevin Durant at both are averaging over 24 points while Klay Thompson and Draymond Green are both adding more than 14.5 points.

Golden State is averaging 114.4 points in the playoffs, which is just a 10th of a point behind Cleveland. Still the Warriors have a point-differential of plus 15.1. They are the only team with a double-digit differential.

With Golden State and Cleveland having split the last two titles, a rubber match was called for almost as soon the Cavaliers lifted the trophy last June.

The problem with predicting a team to upset Cleveland and Golden State is that whichever other teams advance to the Conference Finals they will do so coming out of grueling series.

While Cleveland and Golden State are cruising, the other two series are both tied at 2-2.

In the West, Houston and San Antonio resume play on Tuesday. This series has been interesting in that each game has been won by a double-digit margin.

The Spurs have lost veteran point guard Tony Parker, who ruptured his left quadriceps tendon, for the playoffs while the Rockets will be without reserve center Nene, who tore his left adductor muscle on Sunday.

In the East, Boston and Washington are tied at 2-2 in a series that has been physical and edgy.

The problem for the Celtics and Wizards is that their series cannot end until at least Friday and could go to a Game 7 in Boston on Monday.

The way this semifinal is playing out, it appears that the Eastern Conference Finals won't begin until May 16 or 17 - which means Cleveland will have had more than a week's worth of rest.

Does anyone like a worn down Boston or Washington against a well-rested Cavaliers squad?

The Spurs and Rockets could find themselves in the same situation with their series possibly going as long as May 14.

After taking care of Utah, the Warriors will also have plenty of time to rest before the Western Conference Finals begin.

Anything can happen so it is possible that either the Cavaliers or Warriors, perhaps even both won't advance to the 2017 Finals, but the way the playoffs are going it certainly looks like the NBA is headed for its first rubber match for the championship.

smallwj@phillynews.com

@SmallTerp