Rajon Rondo drives to the basket around Tyrus Thomas during the first game of the Celtics-Bulls playoff series.

AP photo / Elise Amendola

BOSTON – What a difference a year can make.

Coming into last season, many NBA experts considered Rajon Rondo was considered to be the Celtics’ biggest liability. They said the Celtics could not win a world title with the second-year point guard running the offense.

But Rondo and the Celtics proved them wrong by raising championship banner No. 17.

This year, many teammates consider Rondo, not any of the members of the Big Three, to be the team’s Most Valuable Player.

“He’s playing like the best point guard on this planet right now,” Rondo’s backup, Stephon Marbury, said. “He’s doing everything. He’s leading this team. He’s a great leader. He’s done everything.”

“He’s the main catalyst for what we do,” guard Ray Allen said.

Rondo has certainly played like the team’s MVP in the postseason, averaging a triple-double – 24.2 points, 10.2 rebounds and 10.2 assists –– with 3.2 steals and only 2.2 turnovers in 44.2 minutes per game.

Only Cleveland superstar LeBron James (39.0), who averaged 32 points, 11.2 rebounds and 7.5 assists in the Cavs’ sweep of Detroit, has a better player efficiency rating than Rondo (35.0) this postseason.

“I think I’m just focusing in more, especially knowing that guys are going to be out,” Rondo said. “I’m just trying to elevate my game in all aspects of it. I’m not trying to go outside my role. I’m still one of the role players on the team, but I think I have a greater focus this postseason.”

Rondo is performing at such a high rate despite playing with a sprained left ankle. The Celtics hope he can produce another All-Star performance Thursday night at the United Center, when Boston will try to wrap up the series.

“Rondo’s done about it all for us so far,” Rivers said.

Rivers said that Rondo’s success results from a lot of hard work.

“He works,” Rivers said. “You get in what you put in, and he puts in a lot of time. You see him after practice and before practices. You don’t see him in the summer, but he’s in the gym every day. He’s put in the work and he’s taking the deposits out of it, so I’m not surprised by it.”

Rondo’s scoring average has gone from 6.4 as a rookie to 10.6 last season, to 11.9 this season. His assists have jumped from 3.8 to 5.1 to 8.2, and his shooting percentage has climbed from 41.8 to 49.2 to 50.5.

His flaw, critics say, is his lack of a jump shot. But Rivers is quick to point out that Rondo is improving his jumper every day, and if you can average a triple-double in the playoffs while having a “suspect” jump shot, he’ll take that. Rondo’s 50.5 shooting percentage during the regular season ranked third among all starting guards. The reason is mainly his ability to beat his defender off the dribble, get to the rim and finish.

Rondo has knocked down 51.1 percent of his shots this postseason, and 57.1 percent of his 3-pointers.

“I think he’s played at an elite level in this playoff series, no doubt about it,” Rivers said. “And I think he’s played at times this year at an elite level. He’s gone up and down at times, but that is his youth. ... He came into this playoffs with a chip because everyone said he only played well at home last year.”

Rondo said that he is just trying to do everything he can to help the Celtics win.

“Hopefully he can keep playing at a high level, because we are going to need him to with the injuries that we have,” Boston captain Paul Pierce said. “We just have to keep Rondo going. He has the keys to the engine right now. He’s playing MVP basketball right now.”

Rivers said: “Rondo is absolutely terrific. I trust him with the ball all game. He makes great decisions. He plays with unbelievable composure … being as young as he is, and that’s great. He just does so many things for our team … other than taking out the garbage, I don’t know what else we can ask him to do.”

roblee@projo.com