Attacking left-back Seddon joined from Birmingham for an undisclosed fee in July and established himself as first choice, with 32 appearances and three goals.
While Williams was snapped up on a free transfer following last summer’s Fratton Park release and featured 20 times, with two goals.
The duo will come up against their former club on Saturday, when Danny Cowley’s men visit the sixth-placed U’s.
And Oxford Mail’s senior sports reporter, James Roberts, gives the low-down on how the pair have fared.
He told The News: ‘Attacking-wise, people are quite happy with how Steve Seddon has performed since arriving.
‘He has scored three times, while is joint-top assist maker with Gavin Whyte, with five.
‘His dead-ball delivery has been reasonably good, albeit a bit inconsistent, with Billy Boden mainly having set-piece responsibilities at present.
‘Seddon was signed as first-choice left-back, with the hope of having a young back-up on loan from the Premier League to sit on the bench and play in cup games.
‘That never materialised, though, leaving him as the only specialist left-back, although Jordan Thorniley, Sam Long and Anthony Forde could cover.
‘As a result of that, the former Birmingham man has played every minute of every match that he’s been available for.
‘Obviously attacking is his strength and, funnily enough, he scored on his club debut in a friendly against Bristol Rovers – and then competitive debut at Cambridge United!
‘Defensively there have been questions among the fans, however, something we again saw in Tuesday night’s 1-1 draw at Wigan.
‘Seddon lost concentration and let Callum Lang run in behind for the equaliser. It’s frustrating because he has the attributes to be a good defender.
‘Yet attacking-wise there is very little argument that he is a real asset, a marauding left-back with so much energy and probably best suited to a wing-back role.’
Seddon represented Pompey 18 times and scored once during a loan spell from Birmingham in the second half of the 2019-20 season.
As for Williams, he registered eight goals in 85 appearances during his second Fratton Park spell.
Yet, after two seasons, he was among the players released by Cowley during a summer overhaul.
Roberts added: ‘Oxford are well-stocked for the right wing, it's probably the strongest position at the club, but Williams continues to show his versatility.
‘He’s played on the right, linked up really well with Steve Seddon when on the left against AFC Wimbledon, while there were even two games at right-back in August.
‘Overall, he’s not had a huge amount of opportunity, partly through injury, but is demonstrating he’s a really useful squad player.
‘Still, the general mood among supporters is that Williams has been a good signing, with so much energy up and down the flank and being popular around the place with his team-mates.
‘He has also contributed two goals and two assists from 20 games, of which 11 have been starts.
‘There have been injuries, though, with knee and then thigh problems, while he’s also had a spell out through illness.
‘Williams’ preferred position is on the right wing, although he is competing with Whyte and Mark Sykes, while Nathan Holland is on the left.
‘He appeared off the bench in the midweek draw at Wigan and, with players fit, is likely to remain a substitute for Pompey’s visit.’
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