There were wins for Munster and Dragons in round five, but Ulster suffered a shock defeat at Zebre to lose their 100 per cent record.
ZEBRE 27 ULSTER 23
Ulster suffered a surprise defeat as they came unstuck against Italian opponents Zebre at Stadio Sergio Lanfranchi.
In spite of leading at the interval, Ulster conceded 21 second-half points and had to be content with a losing bonus point.
Zebre took an early lead through a Carlo Canna penalty, but Ulster responded with an Andrew Trimble try that John Cooney converted.
A second Canna strike narrowed the gap, but Ulster appeared to have a degree of breathing space by half-time as two Cooney penalties opened up a 13-6 advantage.
Zebre, though, began the second period in blistering fashion, with flanker Giovanni Licata claiming a try that Canna converted, then wing Mattia Bellini posted a touchdown converted by Marcello Violi.
Ulster had it all to do entering the final quarter, but although a Cooney penalty narrowed the gap, Zebre made the game safe when number eight Renato Giammarioli scored his team's third try, with Violi again adding the extras.
The visitors then had the final say through a Darren Cave try that he also converted, but it was a case of too little, too late.
MUNSTER 39 CARDIFF BLUES 16
Munster mined 14 points from a second half sin-binning as they put Cardiff Blues away.
John Ryan and JJ Hanrahan both touched while Cardiff prop Taufa'ao Filise was in the bin, before Hanrahan sealed the province's bonus point and Robin Copeland also scored against his former club.
Cardiff had put the news of head coach Danny Wilson's end-of-season departure behind them to lead 16-13 at half-time, young fly-half Jarrod Evans firing over four place-kicks - including the conversion of Josh Turnbull's 23rd-minute try.
However, Munster went up a couple of gears after the break to put last week's disappointing result in Glasgow behind them. They dominated the scrum and man-of-the-match Ian Keatley, who had converted Conor Murray's first half try, finished with 14 points thanks to six successes out of seven.
DRAGONS 29 SOUTHERN KINGS 13
The Dragons secured their second PRO14 victory in five matches with a bonus-point 29-13 triumph over South African newcomers Southern Kings at Rodney Parade.
Welsh side Dragons never looked like losing from the moment Welsh international wing Hallam Amos put them ahead after six minutes with a try converted by fly-half Gavin Henson.
The hosts piled on the pressure, with hooker Elliot Dee scoring two tries, Amos adding another and Henson booting a penalty and two conversions.
Southern Kings stand-off Pieter-Steyn de Wet landed two penalties before the break and converted flanker Andisa Ntsila's try in the second-half but they offered little else.