Hibino had won just four games across her two previous matches against the Spaniard, a two-time Grand Slam champion and former world number one, though the Japanese started this contest brightly. The world number 78 benefited from an array of errors from the world number 16 to break early on, and impressed as she built a solid 4-1 lead on Court Louis Armstrong.
Muguruza, runner-up at the Australian Open in February, was able to overcome her early nerves however, breaking back down 2-4 and secured a second break at 4-4. The Spaniard missed an easy volley when starting to serve for the set but was in cruise control over that, taking the opener after just over 40 minutes of play.
The tenth seed extended her run of games to seven, consolidating an early break in set two to lead 2-0. Hibino remained firm on serve after that, saving break points down 2-4 and then saving a match point on serve at 3-5, though the Japanese was unable to consistently challenge when receiving. Muguruza faced no break points in the second set and converted a second match point, this time on her serve, to seal a 6-4, 6-4 win.
It was not an entirely convincing performance from Muguruza but her response after falling behind early on was encouraging, and the Spaniard will surely be satisfied with her first match on tour in almost six months. It was also encouraging to see her moving so well following her withdrawal from the Western & Southern Open last week due to an ankle injury.
Flushing Meadows has not been the happiest of hunting grounds for the world number 16 in the past, reaching the second week just once in her previous seven appearances at the US Open, though it looks more than possible she will at least equal her best run this fortnight. She will be the heavy favorite against Tsvetana Pironkova in the next round.