Mercedes ordered Hamilton to pick up his pace after the three-time champion attempted to back Rosberg into the cars behind him, but Horner is surprised that Mercedes would have thought that Hamilton wouldn't employ such a tactic.
"With where they were at, it was just down to those guys, so it was only ever going to be that kind of battle between the two of them," said Horner. "Congratulations to Nico – he's driven a great season, he's a very worthy world champion – but it was naive to think that there would be any different approach with what's at stake."
Horner also backed Hamilton's driving, insisting the former McLaren man did nothing wrong.
"He played completely within the rules – winning the race wasn't going to be enough for him today," said Horner. "He needed cars between him [and Rosberg] and if he'd charged off into the distance that wouldn't have created that possibility.
"He won the race as slowly as he could, it's only like in a football game where a team might protect from the opposition by kicking the ball around and not enabling them to get hold of the ball.
"There's only two drivers competing for the world championship, it was totally obvious that we was going to do that. He didn't do anything dirty, he didn't do anything against the rules and it would be unfair to criticize Lewis for the way that he drove."
Bahrain International Circuit - Winter testing