The trio was all that remained at the head of the race after Spratt (Mitchelton-Scott) destroyed the day's break on the final ascent of the Cauberg, Blaak (Boels-Dolmans) and Brand (Sunweb) the only riders to respond.
Brand opened up her sprint 250 metres out from the line, but Blaak easily answered her compatriot to earn the right to raise her hands in the air.
The victory is Blaak's first wearing the rainbow stripes.
"Awesome! I think this is one of my greatest victories,” she said. "It's really beautiful to win the Amstel Gold Race in front of a home crowd wearing the rainbow jersey."
"When we were with only three, I knew that there was a big chance that I could win the sprint," said Blaak. "Of course I know Lucinda very well, we train a lot together. So I knew she would start her sprint early, because there’s nothing else she could do. It was perfect for me. "
"I have had some great results this spring already, but I still missed that victory. I have been waiting for that a bit. I was very focused on the Tour of Flanders, where I didn’t win myself but we did win with the team, which was great too. But going on to win the Amstel Gold Race, that's just great.”
The break formed on the Keutenberg after 60 kilometres, its 22 per cent grippy bits too much for all but Blaak, Spratt, Brand, Alexis Ryan (Canyon-SRAM), Lotto Lepisto (Cervelo Bigla), Audrey Cordon-Ragot (Wiggle High5), Riejanne Markus (WaowDeals) and Giorgia Bronzini (Cylance).
After initially maxing out at two minutes and 35 seconds, the leaders, with all the big teams represented, held a steady lead of around one minute and 45 seconds.
Blaak thinned out the breakaway with an attack on the penultimate climb of the Cauberg with only Spratt and Brand able to respond. Ryan, Markus, and Cordon-Ragot soon latched back on, but the valiant fight back of Lepisto and Bronzini was doomed when they made it back a lap later at the foot of the Cauberg.
Spratt, who did enough to hold onto third place despite a fast approaching Markus and Ryan, summarised her race perfectly.
“It took a while for a move to go," she said. "And there were three or four moves that I followed before one actually stuck and the fifth one I just latched on to the back and that was the group of eight that stayed away.
“We worked together pretty quickly, and I thought it was a good group with a lot of fast girls, but I was feeling good on the climbs and I decided to wait until the final time over the Cauberg to see if I could split it there.
“I had to go with Chantal and Lucinda, they are both very fast riders and it was in our interests to stay with them and try to get gap over the top, but the end I was cramping a bit up the Cauberg the last time and wanted to keep the pace high and also hoping that I had something left for the sprint.”