Johnny Sexton departed Leinster's opening PRO14 win of the new season early with a calf issue - just three weeks out from the resumption of the Six Nations.
The Leinster and Ireland skipper only lasted 24 minutes at the RDS before making way for Ross Byrne and spent the rest of the first half icing his calf.
Ireland face Italy in three weeks' time before heading to Paris for their final game of the championship, and Andy Farrell will want Sexton firing.
The 35-year-old had played a full part in his province's PRO14 success after rugby's restart after emerging from the lockdown in great shape. Andrew Porter (leg) and Max Deegan (knee) have also emerged as injury concerns, with Deegan's problem seemingly the worst of the three.
Sexton had played a full part in his province's PRO14 success over the past six weeks and after rugby's restart - after emerging from the lockdown in top physical shape.
Moments before coming off, the out-half was instrumental in his side's second try of the night with a skip-pass for Jordan Larmour to score.
As he took his seat in the dug-out, centre Garry Ringrose planted the touchline conversion between the posts.
The defending champions were expected to run up a bonus point victory on their return to action after their Champions Cup quarter-final exit 13 days earlier and it came inside the hour mark.
It took them time to find their rhythm and they lost Ciaran Frawley to an eye injury when he tackled powerhouse Jamie Roberts.
But after a superb James Lowe break, Ringrose cruised in for the opening try in the 17th minute.
And, with Roberts in the sin-bin for a high tackle on Frawley's replacement Timmy O'Brien, the Blues added a quick-fire second as Larmour scrapped his way over.
Lowe added the third in the 32nd minute. Ringrose punched his way into space before Byrne and O'Brien combined and Lowe dotted down.
Show-stoppers Ringrose and Lowe linked for the fourth, the centre spinning a long pass out to the left and the winger beating his man to squeeze over. Byrne landed another tough conversion.
The Dragons produced an eye-catching try of their own with Ashton Hewitt touching down as Josh van der Flier drove him into touch.
But, after James Ryan came close after a superb rip and run, Ryan Baird rampaged over and Byrne converted to finish the scoring, with the excellent Hugo Keenan denied a try at the death.
