"It was emotional," said Jansen, who joined Wanderers on a free on Friday following his release from Rovers.
"I had seven very happy years at Blackburn. Obviously, I didn't want to go but circumstances meant that I had to.
"It was a bit hard and I was worried (before the game).
"I know the fans have been fantastic with me but then to move to Bolton and find myself playing against my old team the very next day was a bit weird.
"I didn't mean it to work out that way, but it was just circumstances.
"The fans were brilliant, though, again and I loved playing for them.
"All along, they've supported me and they've been fantastic with me, and I can't speak highly enough of them.
"(The last few days have) been a mad rush and talk about nerves before the game.
"I'd only trained for one day so I didn't know any set-pieces, I didn't know any systems or anything. But, thankfully, I got through it okay."
Meanwhile, Sunderland defender Alan Stubbs is a target for Rams boss Phil Brown.
The former Bolton and Celtic centre-half joined Sunderland on a free transfer from Everton in the summer but has barely featured in recent weeks.
"Of course I am interested in Alan," confirmed Derby manager Brown, "but I'm interested in players with Premier League pedigree and standards who are not in their first team and Alan falls into that category."