The Foxes, who have already qualified for the knockout phase, are now five points clear at the Group F summit ahead of second-placed Everton's visit to Holmes Park later this month.
Leon Maloney handed Pompey a slim advantage against the run of play after 70 minutes but, with just four minutes remaining, Belgian youngster Eppiah pounced to seal a draw at Nyewood Lane.
City’s line-up included two changes from the 1-0 loss at Chelsea on Friday with goalkeeper Max Bramley replacing Daniel Iversen in the net for Steve Beaglehole’s visitors.
Cup-tied Callum Wright, meanwhile, had to give way for Kiernan Dewsbury-Hall in midfield having already represented former club Blackburn Rovers this season.
Foxes quintet George Thomas, Alex Pascanu, Josh Gordon and Admiral Muskwe were ruled out of the encounter as they recover from injuries.
It was Pompey who threatened early on as Theo Widdrington sent a free-kick inches wide before Bradley Lethbridge nodded it the wrong side of Bramley’s far post from a tight angle.
Bradley Lethbridge then caused concern in the Foxes penalty area when his cross reached Dan Smith in the centre, but his header flew comfortably over the bar.
City’s first clear-cut opportunity came in the 34th minute as the impressive Harvey Barnes located Hamza Choudhury in the centre before the skipper forced Alex Bass into a smart low save.
Pompey first team manager Kenny Jackett was in attendance, meanwhile, to keep tabs on 36-year-old trialist Jonathan Douglas, the former Leeds United and Ipswich Town midfielder.
However, the ex-Ireland international was matched in the middle by the dogmatic performances of Choudhury and Dewsbury-Hall, two of City’s most reliable figures this term.
After the restart, Barnes was able to pick out a gap in the penalty area to test Bass once again, but the 19-year-old ‘keeper was able to get a hand to it.
City were back to their industrious best in the second period with substitutes Liandro Martis and Layton Ndukwu injecting pace into the side.
With just over 20 minutes remaining, Barnes lashed it at goal, forcing Bass to parry it to Eppiah, although the home stopper managed to deny the Belgian.
Despite Leicester's pressure, the deadlock was broken at the other end in the 70th minute as Maloney picked his spot in the bottom corner to complete a quick-fire counter.
While City toiled for a late equaliser, Barnes, Eppiah, Knight and Martis all had attempts blocked in a backed penalty area and they eventually got their reward.
When a low cross from Martis found its way to Eppiah, the Foxes man just had to apply a deft touch to finally get it past Bass.
Who impressed?
Entrusted with a key role in the heart of midfield in Bognor Regis, young midfielder Kiernan Dewsbury-Hall rose to the occasion and led by example to his colleagues.
The Shepshed-based Academy product broke into the Development Squad ranks last term and has cemented his place in Steve Beaglehole’s Under-23s with a string of assured displays.
Where does it leave us?
Now top of Group F by a margin of five points, the Foxes know avoiding defeat against Everton at Holmes Park next month will confirm their status as pool winners.
Leicester are on 11 points, Everton on six (with three games to play), Portsmouth on five and Barnsley on three.
Coming up…
City have just under a fortnight to prepare for the visit of Arsenal to Holmes Park in Premier League 2 on Monday 19 February (7pm kick-off) after the Gunners overtook them in second.
The details…
Portsmouth: Bass, Dandy, Whatmough (Hancott 45), Casey, Haunstrup (Johnston 67), Bedford, Douglas, Widdrington, Lethbridge (Maloney 51), Smith, Chaplin (c)
Subs not used: Collins, Read
Goal: Maloney 70
City: Bramley, Johnson, Wood, Kaba Sherif (Ndukwu 45), Knight, Hughes, Choudhury (c), Dewsbury-Hall, Touray (Martis 45), Barnes, Eppiah
Subs not used: Ughelumba, Yates, Shade
Goal: Eppiah 86
Referee: Adam Penwell