Van der Breggen impressively bridged across to a strong lead group of five riders, including the Australian, who held over a minute's advantage with 43 kilometres to go.
Just a few kilometres later, the reigning Olympic champion powered away on the second ascent of the Igls climb, after Spratt hung tough with her for several hundred metres.
The 2018 Tour of Flanders victor finished the day three minutes and 45 seconds ahead of Spratt, continuing to stamp her and the Netherlands' dominance on international cycling. 2009 world champion Tatiana Guderzo (Italy), 34, turned back the clock somewhat to attack the other chasers behind, claiming the bronze for Italy.
“I didn’t know any gaps," van der Breggen said. "So until the finish line I didn’t believe that I’d be the world champion. I just rode as fast as possible.
"I was doubting if it was too early or not to attack by myself when I did it, but since I took this opportunity, I had to go. I know how difficult it is to win the World Championship, so I’m really happy.”
How the race unfolded
A few surges and flourishes came from several riders after the start of the 156km race from Kufstein to Innsbruck but the early break wasn't formed until about 138 kilometres to go, when Aurela Nerlo's (Poland) attack off the front stuck. She soon had Colombian Ana Sanabria for company and the pair built a lead of around two minutes with 120 kilometres left to race.
Pre-race favourite Annemiek Van Vleuten (Netherlands) crashed at the base of the first gruelling climb of the day, the Gnadenwald, but eventually made it back on with the help of Ellen van Dijk.
First Nerlo and then Ana Sanabria were inevitably caught as several riders fancied their chances when the race hit the circuit section. A dangerous break including van Dijk, Cecile Uttrup Ludwig (Denmark), Lotta Lepisto (Finland) and Guderzo went up the road, gaining a minutes advantage before the first ascent of the Igls climb.
Lucy Kennedy (Australia) went to the front to claw back the advantage, setting a brutal pace up the climb that thinned the peloton down to less than 20 riders and saw the four escapees captured.
American Coryn Rivera surprised many by pulling away at the top of the first ascent of the Igls with 66 kilometres to go and enjoyed a 30 second advantage until Spratt, Van Dijk, Elena Pirrone (Italy), Emilia Fahlin (Sweden), and Malgorzata Jasinska (Poland) bridged across; Spratt, just after surviving a fall into soft grass on a descent.
As news of the leaders dropping van Dijk filtered back to her team mates, the Dutch women first launched Lucinda Brand off the front of the main bunch. Australian Lucy Kennedy, who'd already hit her KPIs on the preceding lap, countered Brand's attack to police but barely held on when it was van Vleuten's turn to launch an assault.
But the Netherlands' played their most dominant card last of all as van der Breggen fired up the afterburners. She jumped across the 40-second gap to the breakaway within the space of a kilometre, immediately dropping most of the riders and eventually seeing off the tenacious Spratt.
From there it was 39 kilometres to the finish and the rest is cycling history.