Van Outen picked up the highest score of the night last Saturday, collecting 37 points for her American smooth with James Jordan.
The West End star and TV presenter also collected another 10 perfect mark to add to the three she earned at the Wembley show.
"Denise is spectacular. She's able to marry the technique with the acting," said Horwood.
"She's very, very special."
Explaining why he hasn't given her a 10 score yet, Horwood revealed: "It wasn't a 10 for me because it didn't say wow. I have to be completely literally gobsmacked.
"A 10 has to represent your point of perfection. If I can see something or think of something that could be done better, then it won't get top marks.
"I know people think that's harsh, but that's judging."
Van Outen is back as the bookmakers' favourite to win the show, ahead of Louis Smith and Lisa Riley.
Strictly continues this weekend on BBC One.
Watch Denise Van Outen's American smooth: