Joan Lascorz drew first blood ahead of the fourth World Supersport round of the season at Assen by edging Cal Crutchlow in opening free practice.
Although the Spaniard experienced a fall mid-way through the session, the battle for supremacy came down to just himself and Valencia winner Crutchlow, Lascorz getting the nod by claiming the quickest time 20 minutes from the chequered flag.
Crutchlow remained second fastest, two tenths behind Lascorz, but another two tenths up on Yamaha counterpart Michele Pirro in third, while Eugene Laverty was fourth quickest on the best of the Hondas.
Garry McCoy showed decent pace on the BE1 Triumph to set the fifth best time, ahead of Anthony West and Kenan Sofuoglu, while local favourite Barry Veneman was in the upper echelons to make it five manufacturers inside the top eight.
Reigning champion Andrew Pitt and fellow Australian Mark Aitchison rounded out the top ten positions.