Lizzie Armitstead believes going off-script paid dividends as she surged to a solo victory at the one-day classic Omloop Het Nieuwsblad in Belgium.

In her first competition since becoming road race world champion last September, Armitstead launched a decisive attack with 10km to go to win the event for the first time.

The 27-year-old had originally been part of a leading duo with Gracie Elvin of Orica-AIS after she lifted the pace in the peloton with 20 kilometres remaining, causing every other rider to fall away.

Armitstead is adamant that two-woman breakaway was an accidental by-product of raising the pace but after dropping Australian Elvin to forge clear for victory, the Brit claims she surprised even herself.

“That wasn't exactly the plan. I was out there way too long. Wow. I'm really happy,” said Armitstead.

"I wanted to break up the group and I ended up on my own. I don't know how it happened, really.

“It wasn't an attack. It was just messing around and people watching each other and not watching me, and so that was really cool."

Armitstead’s Boels-Dolmans team-mate Chantal Blaak sprinted to second place while Tiffany Cromwell of Canyon-SRAM took third.