Max Verstappen/Carlos Sainz a 'highlight' of 2015 F1 season

Both drivers are in their first season of racing in F1 following their promotion from the Red Bull junior driver programme.

Verstappen finished fourth in the last race in Hungary, while Sainz started the season with top 10 results in four of the opening six races.

"They've both driven very well this year," Horner told AUTOSPORT.

"They've been one of the highlights of the season so far, which just proves that giving young talent a chance pays off."

Suggested to Horner the duo could give him a problem when it comes to deciding future driver line-ups, he replied: "Very much so.

"The programme has produced some great talent in recent years, and shows we're not short of talent across the two teams."

Red Bull secured its strongest result of the season at the Hungaroring after a tough start to the campaign, with Daniil Kvyat and Daniel Ricciardo second and third respectively.

"They just need to continue the way they are, to keep pushing each other," added Horner.

"What we saw in Monaco was unprecedented in comparison to other team-mates where Kvyat gave up position to Ricciardo to have a go at a podium.

"It was on the understanding if Daniel couldn't get into a podium position then he would give it back, which he did at the last corner.

"That shows the drivers are working extremely well within the team, and for the team.

"They get on very well. They both grew up in the junior programme, so they know each other pretty well.

"There is a small age gap between the two of them, but it's a very strong dynamic. They're as strong a pairing as we've had."