After 20 years of design and construction, the ATLAS detector has recorded successfully the first LHC collisions last November and December. I will review the performance of the ATLAS detector in this first collision run at sqrt(s)=900 GeV. I will highlight in particular the performance of the main LBL detector responsability: the pixel detector. We now look forward to the 2010 physics run at increased energy and luminosity. I will review how establishing a top quark signal is of great importance for the ATLAS physics program, and will discuss the prospects for measuring the top quark pair cross-section in the next year.