Gillingham manager Mark Stimson felt his promotion-chasing side did not do enough in the final third to beat Rotherham as they went down 2-0 at the Don Valley Stadium.
Debutant Jamie Clarke lashed home the opener after just 25 minutes but it was not until late on that Green capped a superb performance to make the points safe - racing almost half the length of the field before slamming a shot into the roof of the net.
"We played some decent stuff but in front of them, we did not get behind them and test their goalkeeper," said Stimson.
The win ensured the Millers avenged their heaviest defeat of the season - a 4-0 loss at Priestfield in November - but it ended the Gills' run of three consecutive away wins.
Stimson added: "The boys have done well on their trips recently but we knew we were going to come up against a good side here. We always knew it was going to be tough.
"To go in 1-0 down was disappointing. We tried to get in behind them in the second half but unfortunately we conceded a second goal by just not concentrating and doing the basics."
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