Wimbledon champion Muguruza from Spain won her third hardcourt title and ran her career total to five trophys. She stand 39-15 on the season after winning her eighth match at Cincinnati.

Halep, who had little to offer as she lost the rout, could have taken the top WTA ranking from Karolina Pliskova had she won the 56-minute match.

Muguruza played and won her first final in the US and becomes the first Spanish women to claim the title at the Midwest venue.

Romania's Halep was bidding for her second honour of the season after winning Madrid in May; she also played the Roland Garros final against teenager Julia Ostapenko of Latvia. Halep came to the title match without the loss of a set all week and finished runner-up in Cincinnati for the second time after losing the 2015 final to Serena Williams.

Muguruza's matches had lasted a total of nearly two-and-a-half hours more than those played by Halep. Muguruza claimed the opening set in 25 minutes, breaking Halep twice. The Spaniard began the second set with a two breaks of serve for a 3-0 lead with not even 40 minutes gone. The pair last met in 2015 on clay in Stuttgart, with Muguruza now standing 3-1 in the series.

The Spaniard continued her domination as she swept the second set without opposition. Halep drove a forehand wide to end the agony on a first Muguruza match point.