London - In Nemanja Matic and Thiago Motta, Wednesday's Champions League clash between Chelsea and Paris Saint-Germain pitches together two examples of a central component in the Jose Mourinho trophy-winning formula.
Tall, left-footed holding players, Chelsea's Matic and PSG's Motta excel both with and without the ball, fulfilling the principal criteria that Mourinho has come to look for in the 'number six' defensive midfield position.
The Chelsea manager first encountered Motta during his time as Louis van Gaal's assistant at Barcelona, where the future Italy international arrived as a 17-year-old from his native Brazil in 1999.
Ten years later they were reunited at Inter Milan. Motta joined from Genoa and played an important role in the team that Mourinho led to glory in Serie A, the Coppa Italia and the Champions League in 2010, although he missed the European final after being sent off against Barcelona in the semi-final.
Signed by PSG in 2012, he has again become a fulcrum, affording midfield partners Marco Verratti and Blaise Matuidi the freedom to drive forward in coach Laurent Blanc's 4-3-3 formation.
"The position he plays in is perfect for his qualities and for Paris's philosophy," Mourinho said last year.
"They want the ball and in their championship, they have it. In his role, he constructs, organises and sets the tempo."
In building his teams, Mourinho has often used the number six as a cornerstone.
At Porto he had Costinha, another wiry, combative player, and the scorer of the goal against Manchester United during the 2003-04 Champions League that sent Mourinho sprinting down the Old Trafford touchline and into the wider football consciousness.
At Chelsea there was Claude Makelele, the tip of the inverted midfield triangle with which Mourinho swamped the central midfield pairings that prevailed in England at the time.
After Motta, at Real Madrid came Xabi Alonso, whose elegance was often supplemented by the brawn of Pepe for matches against major rivals.
Mourinho believes it is wrong to think of the defensive midfielder as a purely destructive player.
"To me, attacking football happens when Makelele gets the ball and passes it to the central defender, who passes it to the right-back, who comes forward and judges the situation," he explained in the 2006 book The Italian Job.
"If he can do something, he passes forward or runs with the ball. If not, he gives it back to Makelele, who builds the attack again. That is attacking football."
Both Matic and Motta are formidable tacklers, with Matic averaging six per game in this season's Champions League -- more than any other player -- and Motta 3.6.
But they play crucial roles in possession as well, with both featuring among the top six players in the competition's pass completion rankings.
Motta also assumes setpiece duties for PSG, as he did on Saturday when he made his return from a calf injury in a 4-1 defeat of Lens.
A dip in form this season has cast Motta's future into doubt, but Blanc said on Saturday that the 32-year-old remains "a very important player".
After a two-match domestic ban, Matic is also due to make a comeback against PSG, provided he overcomes the ankle injury he sustained during the on-pitch celebrations after Chelsea's League Cup final victory over Tottenham Hotspur.
A Swiss Army knife of a midfielder, the 6ft 4in (1.94m) Serbia international, brought back to Chelsea last season after three years at Benfica, has been variously described by Mourinho as a "giant" and a "monster". And he knows a good number six when he sees one.