But perhaps more should have seen this coming.
Heading into the postseason, a CNN story last month pronounced the Celtics as all but finished, saying "what looked like a promising playoff run has all but faded" because of injuries to Gordon Hayward at the beginning of the season and Kyrie Irving just before the playoffs.
"With Irving unavailable, the Celtics are no longer seen as a contender," our story said.
Ouch. The hazards of the predicting business.
Clearly, that's not the case. It's quite the opposite, really. No matter what happens the rest of this postseason, the outlook for the Celtics has never appeared better.
Smart draft picks, key acquisitions
The team's rise started with general manager Danny Ainge, who has drafted two top-3 picks in Jayson Tatum and Jaylen Brown, as well as first-rounders Terry Rozier and Marcus Smart. He also was responsible for acquiring key players Marcus Morris and Al Horford.
With that young talent, most would have agreed the C's were in a position to contend for a title starting next season. What's so surprising is they're doing it now without Irving, out for the postseason because of surgery on his left knee, and Hayward, whom the Celtics lost in the opening minutes of the season with a fracture dislocation of his left ankle.
Those injuries became an opportunity for growth for the 20-year-old Tatum, the 21-year-old Brown and Rozier, who is all of 24. It's something not lost on veterans like Morris, an elder statesman of the team at 28.
"It gave other guys opportunity to step up," Morris said. "It's very unfortunate that we had those injuries, but no one is going to feel sorry for us at the end of the day, so we have to take our approach of next guy up. That's what we've been doing all season.
"Our confidence level is very high. The younger guys to the older guys, we think we can compete and play with anybody. At the end of the day all the talking is done off the court. Once we step between them lines, we have to compete no matter who we have out there, and that's what we've been doing."
A savvy coach
Another key to the team's success: Ainge hired Brad Stevens, who has shown in just a few seasons that he's one of the best head coaches in the NBA.
Not that Stevens wants to hear that.
"The praise is uncomfortable ... these guys should be getting it all," Stevens said. "We all have a role to play, and we all need to play that role as well as we can."
The Celtics' Aron Baynes, who played under esteemed Spurs coach Gregg Popovich, says there are similarities between the two coaches.
"They're both great with the X's and O's," Baynes said. "They've all figured out more than I've ever learned, so every chance I get and can see some things from them, I'm trying to learn as much as I can.
"Their composure throughout the game is pretty much second to none," he added. "No matter what's going on on the floor, they're so composed in how they are with the team and the message that ... keeps everyone calm."
The byproduct of all this: The Celtics fought past the Milwaukee Bucks and dismantled the Philadelphia 76ers in the first two rounds of the playoffs.
What once seemed improbable -- a trip to the NBA Finals -- is now within reach.
"I think that through the regular season there was so much changes with our group -- guys in and out of the lineup, different injuries, a lot of things like that," Horford said. "Once we've been able to settle down and kind of find what fits this group, I feel like that's what prompted us being better offensively.
"But you've just got to give credit to Coach (Stevens), because he ends up making adjustments ... whichever the matchup is, and giving us those options to go out there and execute on offense."