Leinster held off a late Cardiff Blues onslaught in a 14-13 win at Cardiff Arms Park but it was not enough to keep the province top of the Guinness PRO12.
Cardiff welcomed back five Wales internationals including Alex Cuthbert and half-back pair Lloyd Williams and Gareth Anscombe. Anscombe opened the scoring after just four minutes with a penalty from Manoa Vosawai's break.
Leinster started with six of the Ireland squad as well as a return from injury for Cian Healy. The prop was part of an all-international front row that dominated the early set-piece exchanges and allowed Ian Madigan to level early.
Cardiff had the better of the first half until Madigan's injury-time kick gave Leinster a 6-3 lead at the break.
Anscombe levelled early in the second half but the injury to Allen disrupted the hosts, who were forced to play Wales wing Tom James at centre, and Madigan converted a third penalty.
Neither side could craft an opening until Jack Conan slipped down the blindside of a maul before handing Nacewa an easy finish.
Navidi responded after Jordi Murphy was sin-binned but Patchell saw an injury-time drop-goal attempt charged down as Leinster held out.
The news got worse for Cardiff and Wales, with centre Cory Allen set to be ruled out for several weeks -- including the remainder of the RBS 6 Nations -- with an ankle injury picked up in the defeat.
Connacht won 51-34 at Zebre to move back to the summit following Leinster's brief spell at the top.
Matt Healy helped himself to a hat trick for the visitors, while Niyi Adeolokun scored a brace and Kieran Marmion also went over. All six tries were converted, with Craig Ronaldson and AJ MacGinty adding three penalties between them.
Zebre earned a losing bonus point thanks to tries from Johan Meyer, Kelly Haimona, Dries van Schalkwyk and Federico Ruzza. Haimona converted all four and chipped in with two penalties.
On Friday, Sam Davies kicked 17 points as Ospreys came back from a poor first-half performance to seal a crucial 27-13 win over Edinburgh at the Liberty Stadium.
Sam Underhill and Scott Otten scored tries while Davies added five penalties and a conversion. Edinburgh's points all came in the first half, with a try for prop Allan Dell and eight points form the boot of full-back Greig Tonks.
The Scarlets boosted their play-off hopes by sealing a rare league double over Ulster with a 21-20 victory at the Kingspan Stadium on Sunday, and in doing so traded places with their hosts in the table.
The hard-earned result -- which saw the lead change hands several times in the opening 40 minutes -- saw Wayne Pivac's men move up to third while Les Kiss' Ulster, who began the weekend at the top, slipped back to fourth after claiming a losing bonus point and falling to only their second home league loss this term.
Two first-half tries from Scarlets full-back Michael Collins helped the Welsh side take the hugely valuable win, with fly-half Aled Thomas adding a conversion and three penalties.
Ulster led 17-15 at half-time after superb tries from Craig Gilroy and Luke Marshall both converted by Paddy Jackson, who -- on his debut as captain -- also went on to add a penalty and a drop-goal for 10 of the home side's final total, but it was not enough to clinch the win on Roger Wilson's 200th appearance for the province.
Glasgow Warriors also scored 27 points, edging a high-scoring game with Munster 27-24 at Scotstoun Stadium.
Glenn Bryce's 70th-minute try proved the difference for the home side, who also scored through Duncan Weir and Sila Puafisi. Dave Kilcoyne and Mike Sherry touched down for the Irish province.
Elsewhere, bottom of the table Benetton Treviso closed the gap on third-bottom Newport Gwent Dragons with a 19-17 victory over the Welsh side at Viale Olimpia.
Angelo Esposito, Filo Paulo and Ludovico Nitoglia went over for the Italians, while Hallam Amos and Cory Hill replied for the visitors.