Replacements: James Rael, Finlay Bealham, Aaron McCloskey, Shane Casey, Caolin Blade, Tadhg Leader, Brian Murphy.
Replacements: Gareth Thomas, Ryan Elias, Ben Leung, Nathan White, Jack Evans, Dan Jones, Dion Jones.
Despite being hammered 76-14 by the same Llanelli team in round 1, Nigel Carolan's Eagles side put in a gutsy performance to finish their British & Irish Cup campaign with a third successive home win.
Ronaldson opened the scoring with a well-struck penalty in the 10th minutes. Shortly afterwards, Eagles number 8 Eoghan Masterson was shown a yellow card for failing to roll away.
With the hosts down to 14 men, Llanelli piled on the pressure in the 22 but Connacht did well in defence to keep them out and they reached half-time with a 3-0 buffer.
There were no changes for Connacht Eagles at the break and five minutes into the second period, Ronaldson kicked a penalty from outside the 22 to put his side 6-0 up.
The former Lansdowne ace missed his only shot at goal in the 41st minute, taken from 30 metres out.
It was not until the 55th minute that Llanelli got themselves on to the scoreboard and it was through the boot of their out-half Josh Lewis. Ronaldson responded two minutes later with a third successful shot at goal to make it 9-3.
Lewis missed a chance to close the gap when he kicked a penalty attempt wide and the Eagles went further ahead when that man Ronaldson split the posts from the 22.
As Connacht Eagles looked to tie up the result, replacement scrum half Caolin Blade was unfortunate to have a try disallowed when referee Matthew O'Grady pinged the hosts for 'crossing'.
Llanelli did score the only try of the round 6 fixture in the 75th minute when a grubber kick was chased by winger Aaron Warren who managed to ground the ball over the whitewash.
The conversion was added by replacement out-half Dan Jones to make it a two-point game, setting up a grandstand finish with just four minutes remaining.
But there were no further and Connacht Eagles deservedly held on to make it three wins out of three in Galway, adding to their earlier successes over pool winners Rotherham Titans (27-25) and third-placed Bedford Blues (17-8).
Referee: Matthew O'Grady (England)