CUS shaded a tight Leinster Senior League tussle against King's Hospital, just about chasing down a target of 78 last week in Palmerstown.
From their 30 overs, King's ran up a total of 77 for nine, mainly thanks to the runs of Leinster U-17 development panel duo Daire O'Neill (21) and Ntinga Mpiko (14).
But they were largely kept in check with Adam Craig's three wickets and Barry McAllister picking off two for 15, aided by a particularly economical performance in the field.
It left a fairly manageable total but Mpiko continued his decent day with a spell of three for 24 that left CUS scrambling right the way to the finish line.
Jamie Farrell's contribution of 24 and Craig's additional 20 would eventually aid their win by three wickets though they had plenty of overs to spare in their run chase.
Wesley College, meanwhile, made a confident start to their campaign as they had a mammoth 115 runs to spare over near neighbours St Columba's.
Kirk Shimmins top scored 57 to provide the backbone to the innings and Max Byers chipped in with a useful 38.
In chase, Columba's never really threatened as Alastair Greene claimed four wickets with Muqtadir Shah the sole batsman to hold the fort.
His 19, though, was the high score from a total of 80 for seven.
Castleknock Community College were another side to start in positive fashion as they chased Balbriggan's 84 with plenty to spare, passing the total with just one wicket down.
Sandford Park won the Ranelagh derby with a rare win against Gonzaga College as they amassed an incredible 236 for five, a huge total at this level.
It was well out of reach, Gonzaga bowled out for 140.
It was their second defeat having lost to St Mary's by seven wickets in the first round of the competition, while a fancied St Andrew's saw off St Columba's by nine wickets.