In the last years, the interaction between surface acoustic waves (SAWs) and liquids began to be studied as pumping approach, relying on the streaming effect that drives the fluid flow in the direction of SAW propagation. Closed fluidic-channels were replaced by hydrophilic traces on the chip surface, and the liquid was transported in single droplets by the SAW-fluid interaction. Main issues of such open digitalized microfluidic architectures are the liquid evaporation, and a remarkable sensitivity to surface contamination. On the contrary, closed microchannel environments allow one to incubate and store fluid assays over long times, and to directly control and measure the liquid volumes through the confined channel geometries. In this work we present a novel SAW-driven effect, exploiting the liquid-SAW interaction in hybrid PDMS-LiNbO3 microchannels, which, for the first time, leads to controlled liquid-actuation along the opposite-direction with respect to the SAW propagation. Our devices allow enhancing nebulisation within the fluidic channel, and SAW-assisted coalescence leads to net-fluid drag within the channel itself. The withdrawing pumping configuration was quantitatively investigated and found to be related to the SAW-induced formation and coalescence of droplets within the microchannel. The proposed device geometry appears to be very promising for fabricating integrated micropumps for Lab-on-a-Chip. This approach can be easily extended to more complex microfluidic networks by integrating several IDTs on the same chip to drive fluids along specific paths.