Tottenham head coach Mauricio Pochettino believes Toby Alderweireld and Eric Dier are among the best players in the Premier League in their positions.
Spurs have begun the new year in fourth place, four points off leaders Arsenal and with the best defensive record in the division, having conceded just 15 goals in 19 matches.
Last term, Spurs conceded 53 goals, the same number as Burnley and two more than Hull City, both of whom were relegated.
The transformation has been in part down to the addition of summer signing Alderweireld, who arrived from Atletico Madrid after a loan at Southampton, and Dier's move into a defensive midfield role. Pochettino hailed the duo as among the Premier League's finest players.
"It is obvious after 19 games that Alderweireld is one of the best defenders in the Premier League," the Argentine said in The Guardian.
"I think it is easy to analyse him now. He has given us very good performance and maturity and experience. He is a great boy, a great man."
Alderweireld has formed a formidable central defensive partnership with his Belgium international teammate Vertonghen, a player he knows as well as anyone.
The duo both started their careers in the youth academy of Belgian minnows Germinal Beerschot before moving to Ajax a year apart.
"They are good partners," Pochettino added. "For me, it is important how we work as a team, to try and defend our goal, and to have a very good balance. But it is true that Toby has made a very good impact in the team."
After spending last season rotating between right-back and centre-back, Dier has been a revelation at defensive midfield, starting all but one of Spurs' league matches and earning a callup to Roy Hodgson's England squad.
There has been some speculation that, like Spurs legend Ledley King, the 21-year-old may eventually move back into the heart of defence but Pochettino believes he has found Dier's "real position."
"If we analyse him today he's one of the best holding midfielders in the Premier League," he said. "We are very pleased because he has started to play in a position that was his real position, as a holding midfielder.
"We decided to put him and start to play like a holding midfielder because we saw the quality in the position. We analyse the past and we saw his career and he got to the national team playing like a holding midfielder."