Yes, UA initially inherited the NRT route from PA, but around 97 ISTR (maybe early in the year?) this became one of the first routes they switched to non-stop from SFO. PAL was an absolute wreck of an airline at the time canceling flights constantly because they had not paid their fuel bills or airport fees. The peso got clobbered during the currency crisis killing all air travel demand from the Philippine POS. From memory it was one of the first UA routes to get cut as the crisis worsened.

Around 95 or 96 I was invited by UA to attend a business roundtable in HKG. They explained this new strategy of developing non-stop routes from the US and relying less on the NRT connections on UA metal. Honestly, I thought they did not have a ghost of a chance since it required a lot of long haul aircraft and they were few such capable planes at the time. But I did not fully appreciate how much typical passengers want to reduce connections and the extra costs airlines incur when passengers double and triple connect. Take-offs and landings consume a lot of fuel, the fewer the cheaper the mission for airlines. Good thing I don't run an airline.

It took them 20 years with some twists and turns along the way but UA did it. Essentially they have moved the NRT hub to SFO. They requested Airbus and Boeing to develop planes for these long haul missions and over time they got there. Even SFO-SIN. In another thread I contrasted this with DL's drifting with the tide approach to aircraft. DL seems to prefer waiting to see what the manufacturers come up with and then wait a further number of years to make sure the kinks have been worked out. Leading from behind, I guess.