Central midfield - Sergio Busquets
Sergio Busquets' association with Pep Guardiola began when the latter was managing Barcelona B in 2007-08. On Guardiola getting promoted as the first-team manager, Busquets was promoted as well and the 28-year-old is now one of the best defensive midfielders in the world.
Unlike most defensive midfielders, Busquets is not physically strong or a great tackler. Instead, it is a brilliant combination of awareness, reading of the game and tactical intelligence that makes him one of the best at his role.
His 189 cm frame allows him to play as a makeshift centre-back when needed and he has already won 23 club honours. Further, he was a crucial part of Spain's 2010 FIFA World Cup and Euro 2012 victories.
While the likes of Xabi Alonso and Javi Martinez are definitely top players, Busquets is the perfect player to break down attacks and act as a third defender when the team's full-backs burst forward.
Thus, he picks up one of the two central midfield slots in Pep's greatest XI.
Central Midfield - Xavi
The Barcelona domination in the XI continues as Xavi takes the second midfield spot. While Thiago is a worthy contender, Xavi is legendary in the controller role.
A product of the La Masia academy, Xavi personified the tiki-taka style of football better than anyone else. He controlled games for Pep through his impeccable passing ability and range.
Xavi played the offensive base for his team as they went on to become one of the best sides ever. He won 30 trophies during his time with Barcelona and played a major role for his country as well.
The Spaniard was named as the Player of the Tournament in Euro 2008 and played a key role in Spain's subsequent World Cup triumph and 2nd Euro win. He further holds the record for assisting a goal in two separate Euro finals.
Thus, it is natural for Xavi to form the second-half of the pivot in this XI.