Czech teenager Jakub Mensik stunned top seed Andrey Rublev in straight sets at the Qatar Open on Thursday to reach his maiden ATP semi-final and guarantee a spot in the world's top 100 for the first time. The 18-year-old came through 6-4, 7-6 (8/6) against the fifth-ranked Rublev, a day after defeating three-time Grand Slam title winner Andy Murray. "It's just been an incredible week. From the beginning I played very well and I knew I could play with the big players. It's an amazing feeling to reach the semi-finals after beating those good players," said wildcard Mensik who arrived in the Gulf ranked at 116.