It was a case of what might have been for Pompey as they exited the Carabao Cup at the hands of rivals Southampton.
They dominated the opening proceedings at a packed Fratton Park, with John Marquis striking the woodwork before a couple of goal-line blocks rescued their opponents.
But the impressive Danny Ings proved the difference between the sides, with two goals before the break.
He then provided an assist for Cedric to ensure a fourth round spot, with Nathan Redmond wrapping things up late on.
Kenny Jackett made two changes from the side that were narrowly beaten at Wycombe in the league on Saturday.
Brett Pitman and Ryan Williams both returned to the starting line-up, with Andy Cannon dropping to the bench and Ellis Harrison serving a one-match ban.
Backed by a vociferous crowd – and with the rain bucketing down – it was the hosts who started stronger against their top-flight opponents.
And they almost broke the deadlock on nine minutes, as John Marquis collected Williams’ pass and bent a shot against the post.
Then, after Tom Naylor had been fouled and the visitors struggled to deal with Brandon Haunstrup’s cross, a fierce Pitman effort was deflected narrowly over.
A corner from Haunstrup led to an excellent chance to break the deadlock midway through the first half.
But Pitman’s glancing header was somehow stopped from crossing the line and Christian Burgess was unable to force the ball home from close range.
It had been one-way traffic for much of the half, but Southampton took the lead against the run of play on 21 minutes.
Craig MacGillivray had done well to keep out an initial effort from Ings, but when the striker received the ball back, he curled a fine shot into the bottom corner.
They almost doubled the advantage moments later, as Ings raced through, only to be denied by MacGillivray.
But the danger was not over and Pierre-Emile Hokbjerg’s sent the loose ball towards the net, with a diving Oli Hawkins getting in the way.
Pompey kept battling, though, and a series of good balls into the box caused Southampton problems before Burgess prodded past the post.
The visitors were causing problems on the break and MacGillivray did well to get behind a skiddy shot from James Ward-Prowse.
Ronan Curtis had an effort deflected narrowly off target, while Pitman’s corner was intercepted before it could reach Naylor at the back stick.
But Southampton grabbed a second goal just before the break, as Ings met Michael Obafemi’s low centre and lifted the ball over MacGillivray.
Half Time: Pompey 0 Southampton 2
Several former players were welcomed on to the pitch at the break, with warm applause given to Benjani, Adam Webster, Greg Halford and derby heroes Joel Ward and David Norris.
But it was up to the current crop of Blues to get back into the tie and Curtis had a shot blocked, before Williams skied another over the bar.
For all the passion displayed on the pitch and in the stands, it had not been a dirty contest, with 53 minutes on the clock before Hawkins collected the first yellow card for a foul on Ward-Prowse.
But he was quickly joined in referee Kevin Friend’s book by Pitman, who was penalised for a trip on Obafemi.
Pompey were seeing a lot of the ball without really testing Alex McCarthy and a dangerous corner from Haustrup somehow flashed through a crowded box and out the other side.
The hosts were dealt a blow just before the hour mark, as Hawkins – who had again impressed at the back – limped off to be replaced by Paul Downing.
They continued to push forward and find gaps in the visitors’ defence, but things were not quite landing right for the blue-shirted players inside the box.
And Southampton wrapped things up on 77 minutes, as the ball was cut back by Ings for Cedric to slot home.
Jackett made a couple of substitutions to try to lift the Blues again, with Gareth Evans and Ross McCrorie both brought on.
The hosts kept pushing for the goal that their spirited play deserved, but it was Southampton who instead added a late fourth.
They broke quickly up the pitch and substitute Redmond curled a fine finish past the grasp of MacGillivray.
It did not stop the Fratton faithful from raising the volume levels, though, as they continued to get behind their team for the closing minutes and after the final whistle.
Pompey (4-2-3-1): MacGillivray; Bolton, Hawkins (Downing 59), Burgess, Haunstrup; Naylor (c), Close (McCrorie 82); Williams (Evans 78), Pitman, Curtis; Marquis
Booked: Hawkins, Pitman
Subs not used: Bass, Walkes, Cannon, Maloney
Southampton (4-3-3): McCarthy; Cedric, Bednarek, Yoshida, Bertrand; Ward-Prowse, Romeu, Hojbjerg (c); Obafemi (Redmond 72), Adams, Ings (Long 83)
Goals: Ings 21, 44, Cedric 77, Redmond 86
Subs not used: Gunn, Stephens, Valery, Boufal, Armstrong
Referee: Kevin Friend
Attendance: 18,707 (1,981 away fans)