Sebastian Vettel's seventh win in 12 races this season, and 17th of his career in taking the chequered flag in Belgium on Sunday, means he now has a 92-point cushion over team-mate Mark Webber with seven races remaining.
With the 35-year-old Australian claiming second for the team's 10th one-two, Red Bull are also 131 points ahead of McLaren in the constructors' championship.
Although Red Bull and Vettel are overwhelming favourites to retain the titles they won last year, team principal Horner has stated there will be no let-up.
Asked as to when he would declare this season a done deal, Horner replied: "When it's impossible for anybody else to win it.
"There are seven races to go, still a lot of points available on the board (a maximum of 175 in the drivers' championship and 301 in the constructors').
"Although that was our seventh win this year, our 12th pole, and we've a 100 per cent finishing record, we don't underestimate our rivals.
"There will be no complacency. We're heads down, focused on the next race, and not thinking anything is done and dusted at this point in time.
"We don't alter our approach, absolutely not, and I can assure you Mark still has a free run at it."
Horner hailed the team's success in Spa as "phenomenal" and "a massive result", and rightly so as the circuit has traditionally not been to their liking in the past.
"In many respects it was an unexpected win because power is a dominant factor in Spa," added Horner.
"But that was arguably one of our most competitive races of the season.
"We thought it would favour some of our other opponents in arriving there, so it shows how difficult it is to predict performance.
"But the cars had tremendous pace and the drivers did their bit, which just shows the solidarity we have as a unit."
Next up is the Italian Grand Prix at Monza, without doubt the track where Red Bull have fared the worst over the years.
Horner and his team, however, will head there with their tails up.
Horner said: "We know Monza has been our weakest circuit.
"We also know Ferrari will be strong there, as they historically are, as will McLaren and Mercedes.
"But the result in Spa gives us a lot of confidence, and we will be going to Monza to try to better our previous best result which is a fourth place.
"It is a different challenge to Spa, but given the performance we saw there, it is a good omen for Monza."