Despite leading 19-0 until the final minute of the opening half, the Wizards struggled to overcome a spririted Llanharan outfit, who were fit and played withgreat heart.
Early tries by wing Richard Carter and centre David Hawkins were followed by a second from Hawkins with two converted by Jamie Davies.
Llanharan got on the board with an injury-time penalty by Wayne Jervis, but within five minutes of the restart, Carter went over again for Davies to convert.
Llanharan replied with a try by hooker Alan Williams and Jervis kicked a penalty, though Davies added a further Aberavon score with a penalty shot.
Aberavon were rocked again when flanker Ceri Jones went over for a last-minute try that Jervis converted from the touchline.
In Division One, leaders Maesteg won a local derby by 37-15 against Bridgend Athletic and scored five tries through wing Alun Brown (2), centre Paul Morgan, veteran scrum half Kevin Ellis and fly half Mark David.
David converted three and placed two penalty goals, but the Athletic responded with tries by Gavin Pound and Andy Tollentino and skipper Stuart Morris placed a conversion and penalty.
GB7s women left their England base to train in Wales this week. Olympic Games hopeful Rachael Burford gives WRU TV's Graeme Gillespie her thoughts on Welsh teammate Jasmine Joyce - a 'one touch wonder'
The GB7s women's squad is currently training at Wales' Centre of Excellence where assistant coach Richie Pugh tells WRU TV's Graeme Gillespie some 'tough calls' will have to be made when it comes to finalising the 12 spots for Rio's Olympic Games.
Wales U20's Billy McBryde is looking forward to starting his first game against New Zealand this afternoon in the World Rugby U20 Championship where his side are looking to gain revenge from last week's pool defeat to the Kiwis.