An air carrier Captain reported that during a night visual approach to ONT Runway 26L; his aircraft overtook another air carrier aircraft on approach to Runway 26 as that aircraft's speed was reduced. The other aircraft's crew executed a go-around.

Narrative

We were approaching ONT on a left 45 degree intercept to final for Runway 26L. Another air carrier aircraft was on a right 90 degree intercept Runway 26R. Both aircraft had been cleared for the visual approach and had declared each other in sight. The other jet intercepted the parallel final about a half mile before we did. They were also about 500 FT higher than we were. They began slowing very rapidly and before we could slow we had caught up to them putting us abeam them. They abandoned the approach to the right leaving us free to continue the approach. At no time did we lose visual with them; but it just seemed a little close. I realize that we had assumed responsibility for separation (which I believe we had throughout the approach); but it is almost impossible to judge speed/closure at night from the angle we had to each other. I believe it would have been better operating practice for the Radar Controller to have given speed restrictions or at least advisories. (This seems to be SOP at other airports when given visual even with traffic in sight). Also; the other aircraft was handed off to the Tower just before the Approach Controller read the clearance to a GA aircraft delaying our handoff until quite late in the approach.