After a busy summer highlighted by the signing of Gordon Hayward in early July and a trade for Kyrie Irving in late August, the Celtics considered themselves a legitimate contender in the East. But those plans appeared to have been derailed just minutes into the season, when Hayward suffered a season-ending leg injury in the first quarter on opening night. Without one of their prized acquisitions, it would have been fair to dial down the expectations for the Celtics this season.

Instead, over a quarter of the way through the season, the Celtics have a league-best 18-4 record and look every bit like the best team in the East. After losing their first two games, the Celtics reeled off 16 straight victories. A season ago, they finished with the best record in the East at 53-29, but their +3.1 net rating ranked eighth in the league, an indicator that they were outperforming their actual record. The skepticism followed the Celtics throughout the playoffs, and while they made it to the Eastern Conference Finals, LeBron James and the Cavaliers dominated them in five games, including two victories in Boston to start the series by a combined 57 points.

Last season, the Celtics led the league with 25 wins in games where they trailed in the fourth quarter. A similar trend emerged during the team's 16-game win streak this season. Boston trailed Oklahoma City by 18 points and rallied to win. It put together a 19-0 run in the third quarter against Golden State at home en route to a comeback victory. A few nights later, trailing by 13 points in the fourth quarter on the road against the Mavericks, the Celtics rode Irving's 47 points to an overtime victory.

These improbable victories have invited more skepticism about this year's Celtics, but their success appears much more sustainable this season. Their +6.2 net rating ranks fourth in the league, and Boston's defense is allowing a league-best 98.3 points per 100 possessions, another sign of a contending team. The Celtics' offense ranks in the middle of the pack in efficiency, but Irving has been spectacular as one of the best offensive closers in the league.

Irving is averaging 22.8 points and 5.3 assists while shooting 47.6 percent from the field. Per NBA.com, Irving has been the third-best scorer in the fourth quarter behind only James and Kristaps Porzingis. Irving is a more dynamic player than Thomas, and the Celtics have watched their new starting point guard carry them to victories numerous times. There were questions after Boston traded for Irving about his makeup, and if a team could win with him leading the way. But the Celtics aren't simply relying solely on Irving's brilliance on the offensive end to win games.

In fact, he might not even be their most valuable player so far this season. That honor belongs to Al Horford, the 31-year-old forward who has always garnered less praise than he deserves for being a competent two-way player who executes at a high level on both ends. Horford does all the little things: He sets excellent screens. He's great at rotating on defense. He covers up for his teammates' mistakes. There's a flexibility and dependability about his game that is understated but integral to the success of the Celtics. If Irving is the engine that makes the team go on the offensive end, Horford is their lynchpin on the defensive end.

Per NBA.com, when Horford has been on the floor, the Celtics have a +11.3 rating. Boston has a -2.0 rating when he's on the bench. In Hayward's absence, Horford has been a dependable scoring option. He is shooting 53.3 percent from the field and making 43.1 percent of his threes, of which he's attempting over three per game. Horford's ability to stretch the floor with his perimeter shooting has unlocked a two-man game with Irving that is becoming next to impossible for opposing teams to stop. Switch a slower defender onto Irving, and he can attack the basket for layups and free throws. Commit multiple defenders to Irving, and you give ample space for Horford to take wide-open jumpers.

Irving and Horford have led the way so far, but the Celtics also have arguably the most intriguing tandem of wing players in the league. Second-year player Jaylen Brown and rookie Jayson Tatum, the team's first-round picks from the past two drafts, have fit right in with the team's two stars. Brown has been a lockdown perimeter defender for the Celtics and is averaging 15.6 points per game and shooting over 40 percent from three on offense. Outside of Ben Simmons in Philadelphia, Tatum has been the best rookie in the league. The 19-year-old has looked comfortable on both ends of the floor and has validated general manager Danny Ainge's decision to trade down for him in the draft, playing over 30 minutes a night, averaging 13.7 points and shooting nearly 50 percent from three.

The offensive numbers from Brown and Tatum might regress, but the one silver lining in Hayward's injury is that both players have had to take on bigger roles and have responded splendidly. Boston already looks like it's scored two premium rotation players with huge upside in the past two drafts, and with Irving and Horford playing at a high level, this is exactly the vision Ainge had when he turned over most of his roster this offseason in pursuit of a higher ceiling for his team. Hayward is not expected to return this season, but it's frightening to think about where this team will be if and when he's back on the court at full strength.

The Celtics are the envy of many teams in the league. In an era where we've seen the formation of superteams and franchises that have punted multiple seasons -- whether intentionally or due to incompetence -- to rebuild, Ainge has kept the Celtics on a winning path, built a contender in the present and still has additional draft assets in the coming years to tinker with his roster. In Irving, Horford, Hayward, Tatum and Brown, the Celtics have a very strong core to build around.

There are still concerns about the team's depth and how relying on a rookie over the course of an 82-game schedule might pan out, but those are worries that every team has, whether they're contending or not. The Celtics have spent the first quarter of this season answering a lot of questions about their potential. Even with the Cavaliers on an eight-game winning streak and with James having made seven straight Finals appearances, it's not far-fetched to consider the Celtics as the favorite in the East.