Ruan Pienaar inspired the Cheetahs to victory over the Glasgow Warriors on Friday, while Ulster were too good for the Ospreys.
Tommy Seymour scored two of his team's seven tries as Glasgow Warriors routed Ulster in the first Pro14 semi-final.
After a distinguished career with Ulster and Ireland, Rory Best will call time on his rugby union career after the World Cup.
Edinburgh's Pro14 play-off hopes hang by a thread after a damaging home defeat to Ulster, who extended their own domestic season.
The top two teams in Conference A in the Pro14 were in fine form on Friday as they enjoyed comprehensive victories.
Rory Best has been told he could be out for six weeks, but the hooker has described that as a "magical figure".
Ahead of the 2019-20 season, Ulster have completed a sensational swoop for Ireland prop Jack McGrath from Leinster.
Jacob Stockdale's failure to ground a second-half try proved costly as Ulster fell to a narrow Champions Cup loss at Leinster.
Johnny Sexton will not be risked for Leinster's Champions Cup quarter-final, but Maro Itoje and Stuart Hogg are set to return this weekend.
Bonus-point wins for Glasgow Warriors and Munster mean the top two in Conference A remain three points apart.
The 2019 Rugby World Cup is set to represent Rory Best's swansong, with the hooker "fairly sure" he will retire following the tournament.
Ulster saw out the final 10 minutes with 13 men to inflict a four-try defeat on a beleaguered Dragons side.
Luca Sperandio and Niccolo Cannone scored two tries apiece as Benetton Treviso stretched their unbeaten run to eight games.
Having played for Ulster last week, Iain Henderson has been named in the 34-man Ireland squad to face Italy as expected.
Centre Stuart McCloskey celebrated a century of matches for Ulster by dotting down for the only try against the Ospreys.
There were concerns that Iain Henderson would not feature in the Six Nations, but the lock looks set to play a part for Ireland.