Regan worked his 85-pitch limit over 4 1/3 innings, striking out eight and yielding only two hits and two walks.
"I absolutely thought Danny would be in control in this game," coach David Metzemekers said. "It's what he's done in AAU, in Little League ... he's just been immense."
Zach Smith relieved Regan and efficiently retired the last five batters on only 11 pitches, getting a big assist from shortstop Caeden Dillman.
Danny Regan smashed a two-run homer that went approximately 300 feet to lead Andover American to a 12-0 five-inning run-rule victory over North Andover West in the semifinals of the District 14 Little League tournament on Saturday.
"The umpire behind the plate said it was the longest hit he had ever seen from a Little Leaguer," Andover American manager David Metzemaekers said.
John Metzemaekers went 3 for 4 with three singles and drove in two runs. Thomas Manty went 2 for 4 with a double, single and three RBIs and Zach Smith had three hits for Andover, which managed 16 hits as a team.
Josh Gruenberg earned the win. He worked five innings, throwing just 48 pitches and surrendering just two hits.
Andover National fell to North Andover East in the District 14 semifinals on Saturday. Michael Reilly doubled and singled for Andover National, which got its other three hits from Patrick Hughes, Philip LeBlanc and Andrew Theriault.
Owen Mosher tossed a complete-game two-hitter as Andover Americans took out Tewksbury, 8-1, on Friday.
Mosher struck out seven and needed just 85 pitches to earn the win. Offensively, Josh Gruenburg had a double and a single to pace American. Kyle Vaumbaco and Caedan Dillman each had key hits.
Michael Reilly hit a pair of home runs, but Andover National lost to North Andover West 11-10 on Friday.
Ryan Neal added a homer of his own, while Michael Slattery had three hits. Philip LeBlanc shined on defense at third and 11-year-old Andrew Theriault struck out three in three innings on the mound.