DALLAS -- The Boston Celtics saw yet another game slip away from them, and a 113-104 loss to the Dallas Mavericks on Saturday night puts Boston back to .500 a quarter of the way through the regular season. Celtics guard Marcus Smart quoted Yogi Berra to sum up his frustration with the team's current situation.

"Words can't even explain it," Smart said. "It feels like deja vu all over again.

"We keep saying and doing the same thing after every game. It's getting real annoying ... I don't even know what to say to you guys at this point."

To say this isn't the way the Celtics -- or frankly, just about anyone -- envisioned this team looking through the opening 20 games of the season is an understatement. Yet here Boston is, floundering at 10-10 and already trailing the Toronto Raptors by six games for the top spot in the Eastern Conference -- the one Boston was expected to claim for itself after LeBron James abdicated his throne atop the East by joining the Los Angeles Lakers this summer.

And, as Smart said, the Celtics find themselves saying the same thing game after game. Their offense remains inefficient, mired among the bottom 10 in the league despite a wealth of players capable of filling it up. Too often their first quarters are like the one Boston had Saturday night, as the Mavericks raced out to a 32-18 lead behind some spectacular shotmaking and playmaking from sensational Mavericks rookie Luka Doncic.

Even Boston's defense, which is normally among the league's best -- and is ranked second behind the Oklahoma City Thunder in efficiency over course of the season -- has slipped a bit lately. The Mavericks sliced through the Celtics time and again at that end of the floor Saturday night, knocking down 16-of-41 3-pointers (39 percent) and finding DeAndre Jordan multiple times at the rim for easy alley-oop dunks.

"I thought we were a step slow all night," Celtics head coach Brad Stevens said. "I thought they put us on our heels.

"They made a ton of effort plays, they got a bunch to the rim, and then we couldn't contain the drive ... those drives really hurt us. They turned the corner, laid it in, and had a couple of and-1s, lobs ... those are just killers."

Kyrie Irving struggled in Boston's loss to Dallas, as he was held to only 19 points on 24 field goal attempts. Andy Jacobsohn/AP

The Celtics have been on the receiving end of plenty of those kinds of moments lately. Not only did Saturday's loss drop Boston to seventh place in the East standings, but the Celtics have now lost four of their past five, and eight of 12. Of those four wins, two came in overtime -- including one miraculous road comeback against the hapless Phoenix Suns. The other two came against the equally hapless Chicago Bulls and Atlanta Hawks.

Boston simply hasn't looked like the team it was expected to be entering the season. So what is the issue?

Perhaps there is something to be said for the Celtics having to adjust to the feeling of being the favorite, as opposed to the scrappy underdog.

Throughout the past few seasons, Boston has been seen as a team punching above its weight -- first when Isaiah Thomas was lighting up scoreboards two and three seasons ago, and then last season when first Gordon Hayward, and then Kyrie Irving, were sidelined because of season-ending injuries.

The return of those stars was supposed to turn Boston into a juggernaut. Instead, it has left the Celtics looking like a team stuck between identities, constantly searching for the mix that will unlock its talent and start playing the way it was supposed to from the start.

"It's definitely difficult, because you're going through some things that you're probably not used to," Irving said. "I mean that in terms of having that target on your back. Last year, we got away with kind of just winning games and then going on a winning streak and managing throughout the season.

"But this year having expectations, having that target like you said it's something we all have to get used to as a team. Individually, some of us has been through it. Some teams are going to come at us, some teams are going to put their forearm in our chests and try us. The way we are responding now, we have to respond better."

Some of the team's issues relate to Hayward, and his ongoing recovery from last season's gruesome ankle and leg injuries. Hayward, who sat out Saturday's game as a maintenance day in that recovery, has gradually looked better as the season has progressed. His explosion to the rim simply isn't the same yet, though -- a natural thing to expect, given he didn't play for basically an entire calendar year.

But for Boston to realize its true potential, it needs the Hayward from his Utah days -- the top-20 player in the league, who was a force at both ends of the court -- to return.

Celtics at 20 games under Brad Stevens The Celtics are used to starting better under head coach Brad Stevens, but this season has reversed what was a positive trend. Celtics under Stevens After 20 games End of season Playoffs 2018-19 10-10 ?? ?? 2017-18 17-3 55-27 Lost in Conf. Finals 2016-17 12-8 53-29 Lost in Conf. Finals 2015-16 11-9 48-34 Lost in 1st Round 2014-15 7-13 40-42 Lost in 1st Round 2013-14 8-12 25-57 Lottery >> Hired Brad Stevens as head coach on July 3, 2013

It would be unfair, though, to say the Celtics are at 10-10 through 20 games because of Hayward. There is obvious awkwardness when it comes to the fit and restructuring of the roster after the young kids who led Boston to the brink of the NBA Finals have been shifted into smaller roles this season.

Terry Rozier, who played quite well filling in for Irving during the playoffs, has struggled in a reduced role this season as his backup. Jaylen Brown had one of his best games of the season Saturday night, going 7-for-9 and finishing with 16 points but still is shooting under 40 percent from the field and under 30 percent from 3-point range. And Jayson Tatum, who also played better Saturday, has adopted the bad habit of taking far too many long two-point shots.

It's a mix that, coupled with trying to readjust to the presences of Hayward and Irving in the mix, has the Celtics playing at a level far less than the sum of their parts. And while they search for answers as to why, they're already beginning to lose touch with the teams atop the conference.

That could leave them, once they do figure it out, facing too steep of a climb to get home-court advantage in the playoffs -- making the path they were expected to take to escape the East all that much tougher for them to traverse.

In the meantime, Boston will head on the road to face the New Orleans Pelicans wondering what it is, exactly, that needs to happen for it to snap out of its malaise.

"I don't know," Smart said. "That's the problem. If I knew, we wouldn't be having this discussion, right?

"Once we figure that out, things will start changing. But until then, we're going to continue to get our ass whooped."