On the back of a fine midweek triumph at Notts County, Stevenage cemented second spot with only their second home win of the campaign, to leave the Iron in a precarious 22nd place.
Despite the gulf between the two sides in the table it was mostly even with Mark Duffy and Leon Clarke going close for the visitors but they had no response to Tansey's 75th minute strike.
The win continued Stevenage's unbeaten start to the League One season - which now stands at 11 games - and Smith admitted Tansey's superb strike was of no surprise to him.
"He's [Tansey] out there regularly practising those free-kicks and, even though it was slightly further out than he would have liked, he's so confident, and he works ever so hard at them, that it wasn't a surprise to see it plant right in the top corner," he said.
"It was absolutely plumb. He has got a fabulous technique and it's almost Beckham-esque."