First seed Stefanos Tsitsipas remained on course to potentially challenge de Minaur, securing a 4-1 4-3 (7-2) 4-1 win over Poland's Hubert Hurkacz.
In sets up to four games in the under-21 tournament in Milan, Tsitsipas won 2-4 4-1 4-3 (6-3) 4-3 (6-3).
Tsitsipas, who was announced yesterday as this year's "Most Improved Player", came into Milan as the top seed and won all three of his group matches.
The NextGen Tournament heads for the final in Milano as the top eight ranked male players gather in London for the ATP Tour Grand Finale, while the female players from Czech Republic and the United States are in Prague, for the final of the Federation Cup.
"I had a talk with my coach", explained de Minaur.
He said he didn't know how he recovered from those match points. Even if you play so you don't feel nothing today and the other guy is playing so good, you still can win the match, which is not happening normally when you play the real match.
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The Béticos however finished the first half of the clash with a two-goal advantage heading to the dugout for the break. We want to have the ball so we are able to pressure further up the pitch.
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De Minaur - who began the season at number 208 in the world rankings and reached a career-high 31 last month - also revealed said he had been getting tips from Australia's former world number one Lleyton Hewitt.
"I'm incredibly thankful for the opportunity to play here in Milan and be the second victor of the tournament", Tsitsipas said.
Young gun Alex de Minaur is closing in on another title.
"One thing that I didn't like that much was the towel thing", he said.
'Hopefully I'm going to make the pre-season like I never did before and I can perform well next season and can compete with the top players'.
Last year's runner-up Andrey Rublev required five sets to defeat Spaniard Jaume Munar in the playoff for third with the Russian prevailing 1-4 4-3 (7-4) 2-4 4-2 4-3 (7-3).