The swing feel is a salient feature of jazz music, yet its main psychoacoustical and musical constituents have remained elusive - save the obvious long-short subdivision of quarter notes. In particular, the possible role of microtiming deviations for the swing feel has been a subject of long-standing controversy. Adopting an operational definition of swing we present a study which ultimately demonstrates a positive effect of certain microtiming deviations on the swing feel. We manipulate the timing of original piano recordings to carry out an experiment with expert jazz musicians measuring the swing feel of different timing conditions. Thereby we prove that slightly delayed downbeats and synchronized offbeats of a soloist with respect to a rhythm section enhance the swing feel. Analyzing a set of 456 full solo performances we find that many jazz musicians do use minute downbeat delays and we characterize the dependence of the average downbeat delay on tempo and swing ratio. These results show that systematic microtiming deviations in the form of downbeat delays are a key component of the swing feel in jazz.