Niewiadoma gained a significant advantage over the top of the Cauberg after attacking from near the base of the decisive climb. Marianne Vos (CCC-Liv) was the only one to follow initially, but it was van Vleuten who emerged as the main challenger to the Polish star.
While Niewiadoma continued to push over the final kilometre and a half of flat road to the finish, van Vleuten was closing gradually and the win wasn't assured until just metres remained and Niewiadoma was able to celebrate her landmark victory.
"Yeah of course, I can't believe what happened," said Niewiadoma. "I have so many emotions, I feel like I'm shivering right now."
"I've been wanting so much to win Amstel, dreaming about it and wanting to win so much. It's like a dream come true."
Niewiadoma was fully focused on taking the win and not worrying about the charging van Vleuten coming from behind.
"I wasn't thinking about her (van Vleuten) I was thinking about the finish line," said Niewiadoma. "It felt like the longest two kilometres of my life!"
The race began with an early breakaway, with Australian Shannon Malseed (TIBCO-SVB) representing her squad in the move.
As the climbs grew more regular and the race approached the finish, the field thinned down with gradual attrition and attacks went off the front of the peloton.
Australian Amanda Spratt (Mitchelton-Scott) was present in a number of these moves, present in a group of three with Elisa Longo Borghini (Trek-Segafredo) and Katie Hall (Boels-Dolmans) which attacked with 37 kilometres to go, brought back only by the outstanding efforts of Marianne Vos (CCC-Liv) in the chase.
Spratt also initiated a later as well to join Longo Borghini and Ashleigh Moolman-Pasio (CCC-Liv), going clear with seven kilometres remaining in an attempt to anticipate the final climb.
That final attack was snuffed out due to a lack of cooperation and the peloton went into the base of the Cauberg as a group.
Niewiadoma was the first to launch an attack and have enough left after her effort to just hold off van Vleuten for the win.