The Boston Celtics have had title hopes since the fall, and now they're four wins from sealing the deal.

Then there's the party-crashing Dallas Mavericks, who shocked many on their way to a Western Conference title. Dallas has the best player in the series but is nonetheless a heavy underdog.

Check out our NBA Finals betting preview, featuring key trends, odds and more for the Mavericks vs. Celtics series.

NBA Finals betting preview: Trends and key stats

The grand expectations heaped on the Celtics are evidenced by the spreads they've faced this postseason.

Boston has been favoured by 7-plus points in all 12 playoff games. Its against-the-spread results have been mixed.

Here's a look at some ATS and over/under postseason trends for the Celtics:

• 7-7 ATS
• The over is 8-6
• The over is 6-2 in Celtics' home games
• Boston is 1-5 ATS in its past six games

Contrast that with the Mavericks, who emerged from the West's No. 5 seed to get here. Dallas has been an underdog several times this spring but has thrived in that role.

Here are the ATS and O/U postseason trends for the Mavericks:

• 11-6 ATS (favoured in 10 games)
• The over is 9-7
• The over is 5-1 in Dallas' past six games
• Dallas is 6-1 straight up as an underdog

The Mavs are an NBA-best 34-16 ATS on the road (playoffs included), per Team Rankings. And the team has yet to see an underdog spread as big as the one for Game 1 (+6.5).

But keep in mind that Boston is a beast at home. The team is 43-6 at TD Garden with a +14.4 average point differential.

How they got here

Mavericks: Dallas dropped Game 1 of its series against the Los Angeles Clippers and its series against the Oklahoma City Thunder but ended up winning both matchups in six games. Then the Mavs beat the Timberwolves in five, winning all three games in Minnesota.

Celtics: Boston posted the NBA's best regular season record (64-18) and has cruised to a 12-2 mark in the playoffs — knocking off the Miami Heat, Cleveland Cavaliers and Indiana Pacers. The Celtics' +10.8 net rating is No. 3 among all playoff teams over the past 25 years.

Celtics have been dominant, but have they been tested?

Boston has been exceptional, but its postseason strength of schedule can rightfully be questioned.

• Jimmy Butler (knee) missed the entirety of the first round
• Donovan Mitchell (calf) missed two games in the second round
• Tyrese Haliburton (hamstring) missed two games in the third round

In other words, each opposing team's best player missed 40% or more of their respective series against the Celtics.

That's not even counting stars like Joel Embiid and Jalen Brunson, who missed time for would-be contenders that were eliminated before running into Boston.

The Celtics can only control how they play against their given opponents, and so far the results have been superb.

But given the key injuries that have plagued each of their previous competitors, it's fair to expect the Mavs to be their toughest test.

Can Doncic remain at an MVP pace?

The Mavericks have +180 odds to win the Finals, and Doncic has +180 odds to claim Finals MVP. That should tell you something about what he means to this team.

Dallas relies on Doncic to be its top scorer, passer and rebounder. That's how things went in the regular season and it's still the case now.

Doncic, who led the NBA in scoring (33.9 PPG), has been on fire from 3-point range over his past seven games. He's averaging 4.6 threes per game on 45.7% shooting.

Though he's dealt with a knee sprain since the opening round, don't expect Doncic to crumble the way other stars have against the Celtics. He's averaging more than 41 minutes per game this postseason and has six days of rest before Game 1.

NBA Finals betting preview: How to bet on the series

Boston has been the NBA Finals frontrunner for nearly the entire season, so it's no surprise to see the team favoured now.

But the outright market isn't the only way to back either team in the Finals.

You can also bet on the series spread, with the Celtics holding plus-money odds to win by -1.5 games. The line for total games in the series is set at 5.5 and shaded pretty heavily to the over.

If you like the Celtics' chances of winning the series but don't want to put up with -220 juice, you could consider their Game 1/series double market. Boston has -139 odds to win Game 1 and the title.

Remember, Dallas lost Game 1 on the road in the first and second round this year.