A warning to the Raptors: Objects in the rearview mirror might be closer than they appear.

That seems to be the case with the hard-charging Boston Celtics, who hit the Air Canada Centre on Tuesday for an early-January tilt that is of higher stakes than usual.

Boston was a bit of an underachiever to start this season after getting hyped up by the U.S. media, hovering around .500 for some time, before starters Jae Crowder and Al Horford got healthy. More recently, victories in 10 of their last 12 games have put the team within a game of Toronto for second in the Eastern Conference behind the Cleveland Cavaliers.

Suddenly, the Atlantic Division is a race, with the long-time titan of the division trying to wrest control back from the recent top dog.

While divisions don’t matter all that much anymore, some pride remains involved and banners do go up to commemorate the achievement of finishing first.

After Toronto won the Atlantic for the first time in 2006-07, Boston ruled for five straight seasons (winning a championship and losing another in heartbreaking fashion in that span) before the Knicks surprisingly reigned in 2012-13. Since then, Toronto has won three straight division crowns and is 41-12 (.774) against the rest of the division (including 9-4 against Boston) over the past four seasons.

The Raptors pulled out a tough 101-94 battle at TD Garden a month ago.

“At the end of the day, people struggle with them because they are really good,” Celtics coach Brad Stevens told reporters on Monday about why his team hasn’t found much success against the Raptors.

“(Kyle) Lowry and (DeMar) DeRozan are outstanding players.”

It bears mentioning that Celtics scoring and assist leader Isaiah Thomas had to miss the first meeting of this season due to injury and that games between the two rivals are usually tight affairs.

This time around, Boston will have the red-hot Thomas in the lineup, but fellow backcourt starter Avery Bradley, an excellent two-way player, has been ruled out due to an Achilles injury. That slightly alters just how telling this match-up should be — Boston is 15-5 with its full starting lineup — but then again, Toronto is still without starting small forward Jared Sullinger, the former Boston starter. Perhaps both will be in the lineup for the third of four meetings this season, again at Toronto on Feb. 1.

This has been an extremely difficult stretch for the Raptors, marked by tons of travel (this marks the first time the team has played two straight games at home since Dec. 5-8) coupled with games against quality opponents. Boston’s visit only adds to the grind.

Still, DeMarre Carroll is staying positive.

“(Against Houston on Sunday) we started out good and it’s like our energy, we were just dead,” Carroll told Postmedia. “You could see it in a lot of the guys, even Kyle. He was a little tired, but, I think this is the toughest part of our schedule. If we can sustain this and keep our place where we are at in the conference, hopefully, we can make a run toward the end (of the season) for the No. 1 seed.”

But before they can worry about No. 1, the Raptors need to pull away from No. 3 Boston yet again. Tuesday’s game can get them started on that task.