Peterborough United cruised through to the second round of the Budweiser FA Cup after a comfortable 2-0 win against Exeter City at London Road. Assombalonga ended his goal-drought to open the scoring before Mendez-Laing came off the bench to wrap things up for the hosts.
Posh started brightly and created an opportunity with their first attack, Tyrone Barnett met Mark Little's looping cross from the right but was well saved by Artur Krysiak.
Exeter were happy to allow the hosts to dominate possession, Danny Swanson delivering a free-kick from the left that was easily cleared after 20 minutes.
Barnett was starting to cause the visitor's back-line all sorts of problems with three efforts in as many minutes. The first, a well timed header which was grabbed at the second attempt by Krysiak. A low drive swiftly followed but went harmlessly wide. After Britt Assombalonga pinched the ball deep in the opposition's half, he squared to his strike partner who curled a lovely effort just wide of the post from 16-yards.
Mathew Gill had the Grecians first meaningful attempt just before the end of the first-half, firing a volley wide of Bobby Olejnik's goal.
Two substitutions at the break almost brought the first goal. Less than five minutes in Nthle's cross was only half cleared to the edge of the box but Jack Payne's low drive went straight to the 'keeper.
After 65 minutes both sides were struggling to create any clear openings, a long range effort from Scott Woodman and a long throw-in into the box were easily dealt with by Posh.
On 70 minutes Nathaniel Mendez-Laing and Little combined down the right, the latter crossing low but Krysiak gathered well before Assombalonga could tap-in at the far post.
Seven minutes later it was debutant Hogan Ephraim and Little combining and this time ASSOMBALONGA did meet the wing-backs cross to fire into the roof of the net and give the home side the lead.
The striker nearly doubled his tally for the afternoon moments later, the ball dropping to him in the box but his turn and shot was scuffed wide.
On 79 minutes Posh doubled their lead after a well worked move between Assombalonga and Ephrain provided MENDEZ-LAING
with a shooting opportunity on the right and he struck his shot into the far corner.
With the game opening up, Posh were carving their League Two opponents apart and should have added a third when Mendez-Laing set Assombalonga through but he dragged his shot wide.
As the game went into injury time, a fine one-handed save from the Exeter 'keeper kept Posh from scoring their third of the day. Little with the driving run, and his cross was deflected towards goal before Krysiak saved.
Posh 2-0 Exeter City
Posh: Olejnik, Alcock, Nthle, Brisley, Bostwick, Swanson (sub Ephraim 45 min), Payne (sub Conlon 69 min), Assombalonga, Newell, Barnett (sub Mendez-Laing 45 min), Little. Unused subs: Day, Zakuani, Anderson, Jeffers.
Exeter City: Krysiak, Woodman, Bennett, Baldwin (sub Nichols 78), Coles, Sercombe, Davies, Doherty (sub O'Flynn 45 min), Parkin, Grimes, Gill ( sub Wheeler 80). Unused subs: Pym, Moore-Taylor, Gosling, Keohane.
Attendance: 3,379 (181 Exeter fans)