CDJ Mixing question

[prov]

Hey guys, I was just watching this set from Skrillex at tommorowland, im a newbie in DJing and I was wondering how he made this bpm switch so well:

http://youtu.be/M4N-9hVBW2M?t=17m29s

When he switches from Rock n roll to the birdy nam nam trap remix, you can hear that he starts pitching rock n roll up before making the switch and when its going to drop he crossfades to birdy nam nam's remix and its perfectly in sync, how can you achieve this without using the sync function? (I believe the 2000 nexus weren't available there so he couldn't have used that feature, I can't understand how he pitches up a track, then switches and the other track is perfectly in sync, like "prepared" for the transition).

Any help you wizards?

Thanks!

[Daily Crisis]

It's probably done in a DAW and then pre-recorded.

[RajMahal]

Sounds to me like he creates a loop at the end of rock n roll in which he increases the BPM, applies a low pass filter, then brings in birdy nam nam. I could be completely wrong tho.