Kayal scored after nine minutes, before he set up Israel international team-mate Tomer Hemed for the second on 71 minutes in front a crowd of 12,601 at the Amex.
Albion went top of the Championship with their 2-1 win at Fulham on Monday but made 11 changes to the line-up which started at Craven Cottage. League One opponents MK Dons fielded a near first-choice line-up, making just two changes from their 0-0 draw at Chesterfield in their last match.
Kayal, who had been out since September with an ankle injury, returned to the side and Albion's player-of-the-season last year wasted little time in reminding Seagulls fans of his quality.After the visitors' Chuks Aneke stung the hands of Albion keeper Niki Maenpaa early on, Kayal fired Albion into the lead on nine minutes.
Steve Sidwell won the ball in a challenge with Darren Potter, before Solly March played the ball inside to Hemed and he laid it off for Kayal to drill home, via a post, from 20 yards.
MK Dons had a great opportunuty to level just four minutes later but Ben Reeves sliced the ball horribly wide from just 15 yards.
At the other end, Albion right-back Rob Hunt whipped in two dangerous crosses in quick succession. The first was cleared, before Hemed headed the second well wide from 12 yards.
Brighton continued to look lively going forward and Richie Towell had an ambitious 40-yard half-volley comfortably saved, before Hemed's shot was blocked after excellent play between Kayal and Hunt.
MK Dons were wayward with the openings that came their way during the first half as Albion went into the break with a one goal lead.
The visitors made a bright start to the second half but failed to create any clear-cut chances, before Brighton went close twice in as many minutes. Solly March blazed Sam Adekugbe's left-wing cross over on 53 minutes, before Connor Goldson headed a Jamie Murphy corner onto the roof of the goal.
Murphy then volleyed wide from 18 yards on 65 minutes, before the hosts missed an outstanding chance to double their lead a minute later. Towell beat the offside trap and squared for Hemed but, with just Martin to beat, he blazed over from 12 yards.
The second goal Albion had been threatening came on 71 minutes when Kayal burst forward from midfield and crossed for Hemed, unmarked, to head home from eight yards for his seventh goal of the season.
The Seagulls comfortably saw out the remainder of the game and almost added a late third but Hemed was denied by Martin.
BRIGHTON: Maenpaa; Hunt, Goldson, Huenemeier, Adekugbe; Murphy, Kayal (Ince 78), Sidwell, March; Towell; Hemed. Subs: Ankergren, Stephens, Skalak, Murray, Norwood, Duffy, Ince.
MK DONS: Martin; Baldock, Lewington, Walsh, Upson, Potter, Reeves, Williams, Agard (Powell 79), Aneke (Brittain 83), Maynard. Subs: Nicholls, Rasulo, Furlong, Tshimanga, Thomas-Asante.
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