The match was delayed for 30 minutes due to traffic and floodlight problems and the lights certainly went out on Leeds after an hour, for up until then they were matching their hosts until a collapse in defence led to a humiliation and put a doubt about Reid's ability to carry on as manager at Elland Road.
Mark Viduka had crossed swords verbally with Reid again on Friday apparently after being told he would start from the bench. Jody Morris, also sidelined for disciplinary reasons recently, was restored to midfield and captain Dominic Matteo returned to the heart of their defence following a thigh strain.
He was partnered by Michael Duberry, making his first start of the season. Roque Junior, who has struggled to acclimatise to the pace of Premiership football at the back, was given a new role in midfield, in the absence of David Batty.
Harry Redknapp made a couple of changes with Sebastian Schemmel returning for Boris Zivkovic and Gary O'Neil made his Premiership debut in place of Nigel Quashie.
Dejan Stefanovic put Portsmouth ahead in the 16th minute with a free header from a corner by Patrik Berger, but Alan Smith equalised three minutes later with a crisp left-foot shot.
Until first-half injury time Leeds, who had lost six of their previous seven matches, were on level terms and giving as good as they received.
But then a speculative volley from 30-yards by O'Neil deceived Paul Robinson and Leeds collapsed.
Leeds might have felt a bit hard done by and they started the second half positively with a deep cross from the left by the impressive Saloman Olembe picking out the unmarked Jermaine Pennant, but Shaka Hislop was down quickly at the near post to block the shot.
That was on 47 minutes but then Leeds fell away and it was no surprise when Portsmouth made it 3-1 in the 63rd minute with a right-foot shot from Hayden Foxe which Robinson touched but could not keep out.
O'Neil, playing his first match of the season, finished off a pass from Berger in the 71st minute and the floodgates opened. Berger ran clear after 75 to go around Robinson for the fifth and Yakubu Ayegbeni at the second attempt made it six in the 86th.
Yakubu had been a real handful for Matteo and Duberry all afternoon.
Redknapp said after the match: "Things change rapidly in football. A couple of years ago I thought Leeds were going to dominate for a decade while Portsmouth was a club going nowhere."
To add to Leeds' misery they had Smith, Seth Johnson, Matteo and Olembe all booked for fouls.