Smith, who is on loan from Pompey until the move is made permanent in January, stepped up to convert a last-minute penalty which secured a 1-1 draw for Rangers.
"It was a really strange night for me," he said. "I've never experienced anything like it before to be honest.
"It was strange lining up against the club who still hold my registration but I'm a professional and I had a job to do for QPR."
The result extended Rangers' club-record unbeaten start to the season to 16 matches.
Smith added: "It wasn't the prettiest of matches but you've got to grind out results on the road sometimes and we did that against a very good side."
Source: PA
Source: PA