The Blues’ new striker made his maiden appearance for Danny Cowley’s side, hours after his signing for the rest of the season from Coventry was confirmed.
Walker played 90 minutes in the 0-0 draw against AFC Wimbledon - despite not even training with his new team-mates.
The 25-year-old did a session with parent club Coventry yesterday, before linking up with his new club last night at the team’s hotel.
The former Nottingham Forest trainee went through the details of what was expected of him today – and then partnered George Hirst in attack at Plough Lane.
Walker told of what a hectic period it’s been, but is ready to make an impact at his new home.
He said: ‘I trained with Coventry yesterday and came down after training.
‘We were in the hotel last night and came here for pre-match today.
‘I didn’t train and it’s been very quick.
‘I’m just glad it’s done and I can move on now
‘It has (been a whirlwind) but that’s football and you have to get on with it.
‘You have to get on with it and there’s no excuses not to put the performances in to get the wins.’
Walker completed just his third 90-minute appearance of the season in the Wimbledon draw, with four starts among his 22 Coventry appearances this term.
There was naturally some signs of tiredness and rustiness as he came into the Pompey line-up, but the striker is confident that he will soon shake that off.
Walker added: ‘I’ve come straight into it and played 90.
‘That was good for my legs - now hopefully I can keep it going.
‘I’m 100 per cent fit yet, but I feel like I’ll get there very quickly.
‘It will be good to get the games under my belt and I’m sure the goals will come.
‘There’s new players and they are getting to know what everyone does and everyone likes.
‘I’m sure it will fall in place very quickly.;