Isaiah Thomas scores 29 points for the Celtics, but after a foul on Marcus Smart, Jimmy Butler gives the Bulls the lead at the free throw line with 0.9 of a second left in a 104-103 win. (1:48)

Boston Celtics guard Marcus Smart deserved a better finish to the game.

Twice in the final 30 seconds of Thursday's matchup against the Chicago Bulls, Smart was tasked with guarding All-Star forward Jimmy Butler with Boston clinging to a one-point lead. The first time, Smart smothered Butler before he could even get up a shot, forcing a steal that probably should have iced the game.

But the Bulls got a second chance after their own defensive stand, and Smart grazed Butler's elbow while defending his final-second shot attempt that drew a whistle. So instead of Smart coming up with the big play to secure another Boston victory, the 22-year-old was forced to explain the late foul that helped the Bulls emerge with a 104-103 triumph at the United Center.

Smart initially declined comment to reporters in Chicago when asked about the final sequence but eventually sounded off on what he considered a late whistle from referee Zach Zarba that gave Butler two key free throws with 0.9 seconds to play.

Marcus Smart was surprised that he was called for fouling Jimmy Butler with 0.9 seconds left in the game. Jonathan Daniel/Getty Images

"When Jimmy shot the ball, I heard him scream, 'No foul?' As soon as he said that, the whistle blew and I looked and I saw [Zarba] raise his hand to call the foul and I couldn’t believe it."

Smart, his teammates and even typically unflappable coach Brad Stevens were all enraged by the call. Replays seemed to show that Smart made minimal contact with Butler's elbow, though the Bulls star was adamant that it was enough to warrant a whistle.

Smart disagreed.

"I’m one of the best defenders in this league. I played hell of a great defense right there. I know I did," Smart told reporters in Chicago. "I got punished for playing good D, I guess."

To fully understand Smart's frustrations, you have to recognize that Smart is almost singularly focused on winning games, so having a victory ripped away like that did not sit well with him. What's more, Smart has been playing some of the best basketball of his young NBA career lately and will be thrust into a national spotlight for the wrong reasons in the aftermath of Thursday's game.

On Wednesday night, Smart was spectacular while registering 21 points and eight steals as the Celtics defeated the visiting Philadelphia 76ers. Smart's night was highlighted by a late-game sequence in which he went to the floor and aggressively ripped the ball away from Philadelphia's Nik Stauskas as Boston fended off the pesky 76ers.

Smart didn't play nearly as well on Thursday night and yet you couldn't shake the notion that he was going to make a key late-game play. The Celtics kicked away an early double-digit lead and had to rally back ahead in the fourth quarter.

Chicago had three attempts to pull ahead in the final minute, culminating with Smart fighting through a Taj Gibson screen to smother Butler near the free throw line. If Boston converts at the other end, the story this morning might be focused on whether Smart is playing his way into the NBA's All-Defense conversation.

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Instead, the final sequence will be replayed ad nauseam heading into All-Star Weekend and the whistle will get a second life when the league's two-minute report is released Friday afternoon.

Beyond the foul, Smart has had an excellent February. In nine games this month, Smart is averaging 12.8 points on 46.6 percent shooting overall to go along with 4.2 assists, 4.1 rebounds and 3 steals over 33.4 minutes per game.

"Marcus has had a really good run here," Stevens said Thursday. "Marcus has played really well."

Some will scoff because of Smart's offensive inefficiencies, but he has emerged as one of Boston's most important players during the Celtics' run to the No. 2 spot in the Eastern Conference. Smart has not only started to distinguish himself with improved point guard play but has helped fill the void left by Evan Turner's departure this summer.

Smart is one of the few players the Celtics ought to consider untouchable unless an opponent wants to give away a bona fide All-Star for his services. Even then, it might not be a slam-dunk decision because teams are going to ask for Smart and part of Boston's treasure trove of future draft assets.

There's a case to be made that Smart and a top pick in this year's draft will help this team remain competitive much deeper into the future than splurging on a player who might only marginally aid a playoff run this season.