"Honestly, it seemed like they had 30 players at some point but we did a really good job."
O'Hanlon, who was named player of the match, said the win will be a big boost for the side following a 3-1 defeat to Germany on Friday.
"We really take heart from wins like this. Our team really comes together and really enjoys it. Wins like this really spur us forward."
Merry, along with fellow striker Olivia Shannon off the bench, proved a powerful duo up front for New Zealand while Stacey Michelsen commanded play from the middle of the field in a fast-paced game.
The key moment came in the third quarter when Bingfeng Gu was sent from the field for five minutes following a heavy tackle on Shiloh Gloyn and it didn't take long for New Zealand to capitalise.
The 0-0 scoreline was eventually broken up by Merry in the 32nd minute when a Gloyn long-ball found Merry free in the shooting circle and she quickly took a touch and fired past Chinese goalie Jiao Ye.
New Zealand didn't close out the victory until late in the final quarter when Merry converted a fortuitous penalty stroke which ended up rolling through the legs of Ye who had to re-enter the game after being pulled in the dying stages.
The victory, the Black Sticks' second of their campaign, moves them to sixth in the nine-team competition with a win percentage at 40.