According to anime sales ranking blog Aniran, Lucky star OP Motteke! Sailor fuku has barely missed placing first in the Oricon weekly singles charts by 2,000 units. In first place was Jasmine/Rainbow by V6, selling 68,000 copies, while Lucky Star sold 66,000 copies.
Comparison of previous attempts at getting Oricon 1st:
Happy Material (Magister Negi Magi) - 45,000 units
Hare Hare Yukai (Suzumiya Haruhi no yuutsu) - 35,000 units
Motteke! Sailor fuku (Lucky Star) - 66,000 units
Happy Material and Hare Hare Yukai had the support from the infamous VIP board in 2ch, however both titles did quite badly as compared to Motteke! Sailor fuku, which did not have much support from the VIPPERs. However, Motteke! Sailor fuku had received a lot of attention on the Japanese video sharing site, niconico video, which apparently was very successful in increasing the sales of the single.