Henderson's curling cross was brilliantly met by Gyan, who volleyed home, but the chance almost didn't come as Henderson revealed he had a sudden change of heart after some on-field advice from the gaffer.
"I got the ball on the right and I was thinking about going back, but the gaffer told me to keep going so I did," he explained to safc.com.
"It was great movement from Asa and he put it away really well.
"He came up with a great finish. It was his first chance in the Premier League and he took it brilliantly. Hopefully there's more to come from him too."