The Hornets were on the front foot from the word go and twice came close to taking an early lead, with Giorgi Chakvetadze curling against the crossbar after Luca Kjerrumgaard had headed wide from close range.
But after Ollie Rathbone appealed in vain for a penalty, Watford broke in lethal fashion.
A clever back heel from Chakvetadze – the man who challenged Rathbone in his own box – rolled into the path of Bola whose drilled strike clipped Cleworth and flew beyond the helpless Okonkwo.
Chances kept coming for Watford as captain Imran Louza and Kjerrumgaard both had efforts.
And just as Wrexham started to find their feet in the contest, the hosts doubled their lead as Kayembe curled beyond Okonkwo from the edge of the 18-yard box.
Time and time again, the Welsh side looked vulnerable from counter attacks, and they were relieved to see Nestory Irankunda lash an effort just over from an acute angle in first-half added time.
But Wrexham needed just four minutes after the restart to claw themselves back into the game as Rathbone’s corner was met by Cleworth who nodded beyond Egil Selvik – his side’s first effort on target.
They went close to equalising from another corner as Dom Hyam flicked Lewis O’Brien’s delivery goalwards, only for Mattie Pollock to clear the danger.
Both sides got into threatening positions as the game became stretched in the latter stages.
And after Bola rattled the crossbar with a thumping hit, Bove had the simple task of prodding into an empty to seal victory in added time as Still’s men earned just a second win in six home games.