B777 on final for SFO Runway 28L described a go around event involving a B757 on final for Runway 28R claiming the instructions from the Approach Controller were reversed by the Tower Controller causing the event.

Narrative

We were told by Approach Control that the traffic in sight off our right was slowing to 160 kt and was to follow us. He was for 28R; we were for 28L Approach said; 'maintain 180 to the bridge traffic is at 160 and will follow'. As soon as we checked on with the Tower; about over the bridge; he told us we were to keep the traffic off our right in sight to the runway. This was a complete reversal of what Approach Control had just told us. We scrambled to configure to slow and try and keep the traffic in sight when we received at descend RA. We were in a descent so a slight increase in rate and putting the TCAS to 'RA Only' silenced the warning. The Tower then told the 757 off our right to go around; that the 777 has passed you. The First Officer at that point looked out his window and realized he could no longer see the traffic. We continued to a normal landing. Extremely high workload and a complete reversal of instructions from Approach to Tower led to a very busy approach. I'm not sure if we violated anything or not.