As good as the Boston Celtics have been this season, sitting in second place in the Eastern Conference, they’ve largely struggled against top-flight competition. Heading into Wednesday night, against the other top seeds in each conference — the Golden State Warriors, San Antonio Spurs and Houston Rockets out West, and the Cleveland Cavaliers, Washington Wizards and Toronto Raptors in the East — Brad Stevens’ club had compiled a record of 3-11. There have been mitigating factors, injuries and back-to-back sets and the like, but in general, the Celtics have risen to contention by beating the teams they’re supposed to beat, but had a tough time handling the best of the best.

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Wednesday, then, offered an opportunity to make a statement, with the defending NBA champion Cavs starting a three-game road trip at TD Garden. And despite LeBron James and Kyrie Irving throwing haymakers at their hosts, Boston held fast and declared that even without adding a Jimmy Butler or Paul George at the trade deadline, the full-strength Celtics are good enough to hold their own against the best team in the East … and then some.

A hard-fought and well-played game that featured 19 ties and 24 lead changes went right down to the final minute. After Cleveland answered an Avery Bradley 3-pointer by finding Kyle Korver for one of his own to put the Cavs up by two with 57 seconds left, Celtics All-Star Isaiah Thomas raced for a dribble handoff from teammate Marcus Smart before recognizing a blip in Cleveland’s coverage — defender Iman Shumpert going under Smart’s screen rather than chasing him over it — and decided to call his own number, pulling up from 30 feet and splashing it to regain the lead:

Not to be outdone, Irving — whose ball-handling wizardry had bedeviled the Celtics all night long — went right back at Thomas on the other end, taking him to the baseline before performing some aerial acrobatics to avoid the help defense of shot-blocker Al Horford for a brilliant reverse that tied the game at 99:

Thomas returned serve, beating just-added Cavalier guard Deron Williams off the bounce into the paint and drawing a foul that sent him to the line for a pair of free throws that put Boston back on top, 101-99, with 28.1 seconds remaining. The Cavs had a chance to tie or go for the win on the next possession, but despite two cracks at it, they couldn’t cash in:

Irving went one-on-one with Bradley, in just his second game back from a right Achilles strain but still the dogged on-ball stopper who made the All-Defensive First Team last season, before shaking free and finding just enough room to loft a fadeaway on the baseline. That came up short, but Cavs bruiser Tristan Thompson outworked Horford for his sixth offensive rebound of the game, and 13th overall, to extend the possession by kicking it back up top to James.

LeBron lined up a 3-pointer, but pulled it down to avoid a pair of closeouts — first from Jae Crowder, next from the 5-foot-9 Thomas — before spotting Williams all alone in the far corner. James delivered the cross-court dart, which hit the newcomer’s hands with just over eight ticks left. He raised up and fired as Horford came with a late contest … but the jumper rimmed out and Crowder corralled the rebound, forcing James to foul him with 4.2 seconds remaining.

Crowder calmly knocked down both his freebies to cement a thrilling 103-99 win that gave the Celtics their first win in three tries against the Cavs this season, and drew them within three games of Cleveland for the top spot in the Eastern Conference.

All season long, Thomas has drawn praise for being the league’s premier late-game scorer, “Mr. Fourth Quarter,” “The King in the Fourth.” On Wednesday, though, Thomas did the bulk of his damage in the third, scoring 11 of his game-high 31 as he went back-and-forth with Irving in a duel of high-end shot-making:

Thomas made just one field goal in the final frame, that killer stepback 3 to take a 99-97 lead. But don’t let the fact that Thomas didn’t put up double-digit points in the final 12 minutes make you think that the Cavs stopped him. He won’t allow that:

Thomas still carried the quarter, breaking down Cleveland defenders off the dribble and prompting aggressive help — including, on a couple of occasions, perhaps overly aggressive help from LeBron — that left Bradley and Crowder open on the perimeter. Rather than try to bull his way to the rim for finishes in traffic, Thomas made the right reads, pitching the ball back out to his shooters and having faith that they’d make shots. They repaid his trust.

James, too, showed plenty of trust on the Cavs’ final possession when he decided not to take it himself, but rather to pitch the ball to the wide-open Williams in the corner for a potential game-winner in his first game after joining Cleveland on Monday.

“I saw Crowder running to me, he jumped and then I saw [Thomas] running toward me,” James said after the game. “I saw D-Will naked in the corner, so I gave him an opportunity and he just missed it. We got the shot we wanted.”

“I know, it was a great moment — it was set up perfect,” Williams told reporters after the game, which saw him score four points on 2-for-8 shooting with two rebounds and two assists in 24 minutes in his first game action since Feb. 15. “I did everything but make it. Wide-open. Wide-open. Felt good, looked good, just didn’t go in.”

As a result, the Cavs fell short for the first time this season after holding a fourth-quarter lead — they had been 15-0 in games during which they’d held a final-frame advantage — despite James turning in his seventh triple-double of the season, with 28 points on 10-for-21 shooting to go with 13 rebounds, 10 assists, one block and one steal in 40 minutes of work:

… and Irving pouring in 28 of his own on 10-for-19 shooting in 28 minutes:

They fell short because Thomas had help. Crowder chipped in 17 points and 10 rebounds. Horford, often derided for insufficient counting stats despite the major impact he makes as a defensive anchor and supplementary playmaker, came one point shy of a triple-double, with nine points, 10 rebounds and 10 assists.

Marcus Smart had nine points and eight assists, and hustled to force a couple of big charging calls against Cleveland’s Derrick Williams in the fourth quarter. Rookie Jaylen Brown competed his tail off on defense and on the defensive glass. Kelly Olynyk added 10 points and stout defense off the bench. Boston worked overtime as a team, holding Cleveland to 40.7 percent shooting, winning the rebounding battle 47-41 and dishing 28 assists on 36 made baskets.

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All told, the version of the Cavs that has James and Irving on the ball, Thompson beasting in the lane, and starters Kevin Love and J.R. Smith back from injury to go with Williams at backup point guard and forthcoming signee Andrew Bogut in the middle probably just has too much talent for Boston to overcome in a seven-game postseason series. But for the Celtics, Wednesday offered a proof of concept all the same — that Thomas’ drive-and-kick game can be the starting point for a means of distorting Cleveland’s defense, that Boston’s small-ball/spread-the-floor lineups can marshal enough firepower to make the Cavs pay for loading up on Thomas’ drives, and that, on the right night, the combination of Thomas’ shotmaking and an all-hands-on-deck defensive approach can topple even the best player in the game.

Whether the same approach can pay dividends in the postseason, when Cleveland could devote more resources to trying to trap Thomas and get the ball out of his hands before he can make a play, remains to be seen. But the Celtics will cross that bridge when they come to it. For now, just getting a well-earned win over the conference’s top dog, and proving to themselves they can hang with the champs, is enough.

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Dan Devine is an editor for Ball Don’t Lie on Yahoo Sports. Have a tip? Email him at devine@yahoo-inc.com or follow him on Twitter!

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