Both were signed at the start of this season and both have gone on to play important roles in helping their clubs make it to Saturday's Champions League final in Porto.
AFP Sport looks at the impact of Ruben Dias on Manchester City and his fellow centre-back Thiago Silva's importance to Chelsea.
- Dias: City's transformative signing -
What could turn out to be Manchester City's most glorious season started inauspiciously with their first home game of the campaign ending in a 5-2 thrashing from Leicester City. City's swift response was the signing of Dias for a club record £62 million ($87m).
"If this doesn't work, I think it is possibly the end of the Pep project," former Liverpool defender Jamie Carragher said on the day Dias arrived in Manchester.
Instead Dias, now 24, has not only finally filled the void left by Vincent Kompany's departure in 2019, but he has had a transformational impact on those alongside him.
England internationals John Stones and Kyle Walker suddenly look like the £50 million players City bought in Guardiola's early days.
The strapping Portuguese international had no problem adapting to the physicality of English football, but it is his leadership in his first year in a new country that has caught the eye.
"Opponents will always score, because they are good, but we don't give them easy chances -- that is the big improvement of Ruben Dias," said Guardiola in March.
"He's a central defender who leads the line and leads the team. His performance and decision making are good, but he also helps other players make good decisions -- that is how you become an incredible defender."
Thanks to Dias, City have been the defence in the Champions League this season, conceding four goals in 12 games.
Likewise a 15-game winning run that saw City soar from mid-table to a commanding lead in the Premier League between December and March was built on the foundations of 10 clean sheets.
Last week, Dias became the first defender in 32 years to win the English Football Writers' Association player of the year.
"I think me receiving this prize is the major example of how our team works, the way we build our game," he said.
- Silva's close relationship with Tuchel -
Silva, 36, is at the opposite end of his career to Dias, but it is his wealth of experience and relationship with coach Thomas Tuchel that makes him so valuable to a Chelsea side whose success in 2021 has been built primarily around an outstanding defence.
Last year the Brazilian captained Paris Saint-Germain as they lost 1-0 to Bayern Munich in the final in Lisbon.
It was his last game for the club as Silva's contract was not extended, much to the disappointment of Tuchel.
"The decision doesn't matter. He will remain my player. He is in my heart and it was incredible to go through this with him," Tuchel said nine months ago.
Silva promptly joined Chelsea on an initial one-year deal, but was reunited with Tuchel in January when the German replaced Frank Lampard in the Stamford Bridge dugout.
It remains to be seen if Silva will still be there next season, and he actually played more games for Chelsea under Lampard than he has under Tuchel.
Injuries ruled him out of most of the new coach's early games, including the last-16 tie against Atletico Madrid.
An animated Silva instead spent the second leg of that tie marshalling Chelsea's defence from the stands, and his experience has helped bring out the best in Antonio Ruediger and Andreas Christensen alongside him with Tuchel overseeing 18 clean sheets from his first 24 games.
Tuchel also knows that, with so many young players in his squad, Silva's experience is invaluable.
"I am pretty sure that for 'Thia' it is a big advantage to come back to the final, to have this experience again and learn from the year before," Tuchel said of Silva, who is returning to the city that was his first stop in Europe in 2004 when he played for Porto's reserves.