Anthony Stewart headed home a dramatic equaliser four minutes into injury-time to earn the Chairboys a 2-2 draw.
Gareth Ainsworth made five changes to the Wanderers side with Sam Wood, Gary Doherty, Matt Spring, Billy Knott and Dean Morgan coming in. Josh Scowen (groin), Charles Dunne, Stewart, Max Kretzschmar and Steven Craig were the men to make way.
Wood (groin) and Knott (illness) were unavailable for Saturday’s defeat at Dagenham, while there was also a return to the squad for Jo Kuffour, who had been ruled out with a thigh problem.
The hosts started well and Ricky Holmes’ mis-hit shot from Danny East’s cross forced Matt Ingram into a smart stop low to his right in the seventh minute;
Wanderers’ first effort came in the 12th minute, but Marvin McCoy’s 25-yard flew well wide after the hosts failed to clear their lines.
Ainsworth’s men were starting to see much of the ball and Paris Cowan-Hall saw strike blocked by Johnny Ertl, before Stuart Lewis’ first-time shot stung the palms of Trevor Carson after a neat passing move down the left.
Chairboys’ improved play was rewarded in the 21st minute when McClure took advantage of some hesitant Pompey defending, turned his marker before clinically drilling low past Carson and into the far corner.
The home side responded with Jed Wallace trying his luck from 20 yards, but Ingram was well positioned and made a comfortable stop.
Poor defending from Joe Devera allowed McClure to find Wood on the edge of the area in the 30th minute, but he didn’t strike the ball cleanly and it went harmlessly wide.
A serious-looking injury halted the game just past the half-hour mark as Danny East fell awkwardly after challenging Morgan. After a prolonged spell of treatment the right-back was stretchered off and replaced by Bondz N’Gala.
Portsmouth’s frustrations were beginning to show and Jed Wallace was booked for a needless challenge on Morgan near the touchline as the game neared the start of eight minutes injury-time. Spring’s resulting free-kick was flicked on by Morgan to McClure and his header was somehow parried behind by Carson.
Pompey caretaker boss Andy Awford made his second change at the break, bringing on the experienced David Connolly for Wallace, while Ainsworth kept things the same for the second half.
The hosts again started brightly, but without threatening Ingram’s goal and Cowan-Hall nearly broke through eight minutes after the restart when he reacted quickest to Sonny Bradley’s poor touch, but Dan Potts recovered well to deny the former Portsmouth man.
Ingram did well to parry away Holmes’ dangerous cross soon after, but the ball fell to Andy Barcham, whose shot was blocked by McCoy. Portsmouth kept up the pressure and found Connolly in the area, but again Blues’ No. 1 was equal to the effort.
Superb defensive work from Doherty and Lewis crowded out Barcham moments later after the winger had threatened to break through after initially picking the ball up on halfway.
Pompey were enjoying their best spell of the game with Devera seeing a fierce drive headed behind by Doherty, before Shaun Cooper shot narrowly wide from 20 yards.
Matt Spring saw a low 25-yard drive saved by Carson as Wanderers pushed forward to alleviate the pressure that had been building.
Portsmouth were handed a lifeline in the 69th minute when Wood was adjudged to have fouled Connolly in the area. The striker took the spot-kick himself, but Ingram guessed the right way to parry before Ryan Bird’s follow-up was superbly deflected behind.
However, the hosts weren’t made to pay for their miss and levelled three minutes later when Barcham was found in the area by Homes and rifled a shot past Ingram.
Blues responded well, but McClure was unable to get the ball out of his feet quick enough to capitalise on a mix-up between Carson and Potts.
Ainsworth made his first change 10 minutes from time with Stewart replacing Johnson and Spring tried his luck from near the halfway line two minutes later with Carson way out of goal, but his ambitious effort drifted wide.
The home side took the lead with six minutes remaining when substitute Agyemang eluded his marker to meet Holmes’ free-kick and powerfully head past Ingram.
Wanderers pushed for a late leveller as the game entered in injury-time and it came in the dying seconds. Stewart, who was only available to play after his red card from Saturday was rescinded on appeal, met Kretzschmar’s corner and emphatically headed past Carson in front of the travelling Wycombe faithful to earn a deserved share of the spoils.
Wanderers: Ingram, McCoy, Wood, Doherty, Johnson (Stewart 80), Spring, Lewis (c), Knott (Kretzschmar 86), Cowan-Hall, Morgan (Kuffour 86), McClure.
Subs: Horlock, Dunne, Arnold, Craig.
Portsmouth: Carson; East, Potts (N’Gala 37), Devera, Bradley, Wallace (Connolly 46), Ertl (c) (Agyemang 78), Cooper; Barcham, Holmes, Bird
Subs: Sullivan, Painter, Padovani, Ferry.
Attendance: 14,942 (681 Wycombe)