Their partnership record is one of the most prolific and successful in England's Test history.
When batting together, they have amassed 3362 runs in 54 innings at an average of 65.92 - bolstered by their 13th 100-run partnership in the second innings at Trent Bridge.
Today's (and last night's) dig moved England from a deficit and real peril at 11 for two to the relatively strong position of a 56-run lead. Pietersen's dismissal when on 64 only served as a reminder of how fragile that advantage seemed without both men in the middle.
Few would compare the pair's batting styles - Cook is still the more obdurate, doughty of the two, while Pietersen is the player capable of flair. It is perhaps a sign of their development as players that both have the capacity these days to play more like the other - KP was solid and patient at Trent Bridge, Cook has expanded his repertoire of shots as his career has progressed.
Pietersen has fallen out with all and sundry at various points, and will never sit well with some England fans because of a cocktail of his origins and his brashness. Cook, meanwhile, may be many things, but he will never be divisive.
And yet their record at Test level before this game is astonishingly similar:
Two players. To all intents and purposes, the same record. Two very different perceptions.