Andrew Heffernan is one of two standout pitchers for South Portland as the Red Riots try to defend their Class A title. Derek Davis/Staff Photographer

The high school baseball playoffs start in earnest Monday and Tuesday with regional round-of-16 games. In classes A, B, and C, a clear short list of favorites has emerged.

But, as last year showed when top-seeded Yarmouth in Class B and second-seeded Scarborough in Class A were bounced in the first round (by No. 16 Gray-New Gloucester and No. 15 Portland, respectively), baseball doesn’t always go as scripted, especially if the underdog gets a couple of quick runs and a strong pitching performance.

“There are a lot of teams out there and a lot have at least that one (pitcher) who can be tough,” said Scarborough Coach Wes Ridlon. “Last year, we experienced that against a strong, gritty Portland team. And our guys are going to remember that. You have to bring it every game. You can’t take a day off and nothing is going to be handed to you.”

Recognizing that some team will surely surprise, here’s who we think are the southern Maine teams with the best chance to be playing when state championships are at stake on June 18, along with some dark horse candidates.

CLASS A SOUTH

The top four seeds have established themselves as a slight cut above the rest in a competitive region.

No. 1 Thornton Academy (15-1) has won 12 straight games since an early loss to No. 6 Westbrook. The Trojans have beaten every other team in the region and have a potent offense (8.6 runs per game) to go with a 1-2 pitching rotation of senior right-hander Cody Bowker, the state’s Gatorade Player of the Year, and lefty Josh Kopetski.

Bowker (.490, four homers, 29 runs) sets the table as the leadoff hitter and Brady Graffam, John Rohner and Nic Frink have produced in the heart of the order.

“You’re going to have to be able to score runs,” said Thornton Coach Jason Lariviere. “There’s going to be some good pitching we’ll run into.”

No. 2 Falmouth (14-2) has depth in its pitching staff and has started to produce more offensively. Defending champion South Portland (13-3), the No. 3 seed, could use more consistent offense but has the shutdown pitching of Andrew Heffernan and Nolan Hobbs.

No. 4 Scarborough (12-4) has won seven straight, four by shutout, including a 2-0 win against South Portland in the regular-season finale. The return of sophomore Harrison Griffiths from an injury has bolstered a pitching staff that had already been getting great effort from freshman Erik Swenson (6-0) and Ben Seguin. Senior shortstop TJ Liponis, who started as a freshman on the 2019 championship team, is leading the offense, playing great defense and “playing some of the best baseball of anyone in the league,” Ridlon said.

Scarborough’s first-round opponent is No. 13 Bonny Eagle. The Scots (5-11) represent the underdogs with an upset shot, thanks to senior pitcher Mason Ryan and a season of growth for a young team that won three of its last five games and took both South Portland and Falmouth to extra innings.

Another interesting first-round game has No. 10 Noble (7-9) at No. 7 Portland (9-6-1). Noble beat Portland, 6-3, on April 30 at Hadlock Field when the Bulldogs were in the midst of an 0-4-1 stretch that they followed with a six-game winning streak.

“Noble, offensively they’re solid and they’re going to battle you,” Ridlon said.

Lariviere added: “Every team has a strength. Portland hits really well. They put on some of the best at-bats against Cody (Bowker) this year.

CLASS B SOUTH

Greely (15-1), behind senior left-hander Zach Johnston, is clearly the team to beat. Ten of Greely’s wins have been shutouts, including six straight to end the regular season.

Plus, the Rangers have produced offensively, winning six games by the 10-run mercy rule and averaging 8.9 runs to back Johnston and senior No. 2 starter Ryan Kolben. Both Johnston and Kolben have thrown two no-hitters this season.

The one team that has shown it isn’t cowed by Greely is No. 4 Yarmouth (10-6). The Clippers won the first meeting between the teams, 7-2, and lost 2-0 in the rematch, getting four hits and one walk off Johnston.

A third meeting between Greely and Yarmouth, which would be in the semifinals, seems a strong possibility.

No. 3 Freeport (12-4), the defending regional champion, is in the opposite side of the bracket and will have to beat No. 14 Gray-New Gloucester for a third time and then, if seeds hold, No. 6 York (11-5) in the quarterfinals. York is 8-2 after a sluggish 3-3 start. Both losses in that stretch have been by a run, 4-3 at Greely and 8-7 to Cape Elizabeth at home.

The Class B South tournament features teams from the Western Maine Conference and Kennebec Valley Athletic Conference. The KVAC group is led by second-seeded Erskine Academy (14-2). No. 9 Morse (7-9) has Gavin Baillargeon, another pitcher with two no-hitters this season.

CLASS C SOUTH

Lisbon is 16-0 and has a history of success, having won the state championship in 2019 and the regional title in 2017. The Greyhounds have allowed one or zero runs in 13 games.

But No. 2 Sacopee Valley is 14-2, and its only losses were on May 7, when it dropped both games of a doubleheader at No. 6 Maranacook (11-5). Since then, the Hawks have won seven straight, including 9-5 and 11-4 wins against No. 4 seed Waynflete/NYA (12-4).

No. 3 Mt. Abram, also 14-2, has won 10 straight since losing to Lisbon on May 9. The top 10 teams in the tourney have a winning record, including defending regional champion and fifth seed Monmouth Academy (12-4).