I might be misremembering, but the initial core series (core 2 duo/quad) was still a bit behind AMD's Phenom line. Core was definitely better than the old netburst architecture, but I don't really remember Intel regaining dominance until the core i series/AMD FX.
This was also like high school/college for me, so I could be way off.
This was also like high school/college for me, so I could be way off.