Some prior history: Monday about 1.30pm 8101 arrived at Glenfield via the EHDN and began signal testing, starting with the P4 road and trips out to around MF station at a guess. After a couple of trips between GD1 (EHDN) and MF (using the same track), it was switched to the lower end of the Leppington DN ramp. From there it did multiple passes to the P3 platform, testing (AFAICT) the point, catchpoint and related DN Main start signal, which is about when I left it due to declining day and declining weather.
The first 'business' train over the NFO was the 4.05am from Campbelltown today, a K Set with C3548 as lead power car. On approach to Glenfield we were routed to P1, and during our brief stop the guard announced our 'first' as about twelve people wearing PPE (orange vests/white hats) joined the train and three others similarly attired (but one equipped with a camera and tripod) boarded the drivers cab; I assume they were 'SydneyTrains' people. We left near enough to 4.20, and didn't need a flying start at the 'hill' to top it at about 4.23... the view was a non-event at that hour, but did notice a 'drop' on leaving the top of the 'block'. I and all the people previously noted alighted at Holsworthy and after a short wait we all boarded a Campbelltown train that used P4 as expected. We passed a south-bound train enroute to Holsworthy, so cannot claim that as a first use of P4 also.
From what I have come to understand, after 4pm, the test loco 8101 came across to P3 and completed testing between there, GD26 and P4. Test loco 8141 tested through from Casula to Ingleburn on the down and then came back to P1 on the Up. 8101 then went wrong road from P3 to Ingleburn, while 8141 went to Casula on the Up. There was a bit of a spell while points that were remaining booked out were clipped and spiked, then 8141 came back from Casula to complete more testing around Glenfield, before going back to Casula.
8101 then came through from Ingleburn through P3 and over the northern flyover to take (from what I can gather) honours of the first 'train' over the flyover at around 7pm. 8141 came back to Glenfield for more testing, with all testing being done by around 9pm.