Weir was on the receiving end of a head-high tackle from Motu Matu’u, which earned the hooker a red card after only 34 minutes and left his side to play the whole of the second half a man short for the second away league fixture in a row.
Prop Ollie Hoskins was the offender at Bristol earlier this month when Irish went on to secure a 27-27 draw, but they could not repeat that remarkable feat against Irish on Saturday.
Weir scored a try for Worcester and kicked two penalties and a conversion. Jono Lance was the other Warriors scorer with a try and conversion, while Stephen Myler responded with two penalties for the visitors.
Worcester, anxious to impress the first sell-out crowd at Sixways since April 2018, began strongly by enjoying an extended period of pressure.
Francois Hougaard and Cornell Du Preez were the protagonists in testing the Irish defence and the hosts looked to have taken the lead in the sixth minute when Tom Howe crashed over, but TMO replays showed that the wing had lost possession before grounding the ball.
Warriors continued to have the better of the opening period but it was Irish who were first on the scoreboard when Myler kicked a 40-metre penalty.
A poor kick from full-back Alivereti Veitokani surrendered possession to give Warriors a platform in the opposition 22, and from there the space was created for Weir to score the opening try.
Weir converted before adding two penalties in quick succession as his side continued their first-half dominance.
A couple of attempted clearances by Hougaard were charged down to raise Irish hopes, but these soon faded when prop Allan Dell was yellow-carded for charging dangerously into a ruck before Matu’u was sent off.
Weir received treatment before kicking for the corner as Warriors elected not take an easy three points, but it did not pay dividends and the score remained at 13-3 as the interval arrived.
After the restart, Myler kicked a second penalty before Weir was replaced by Lance with 30 minutes remaining as the home side struggled to break down a stubborn Irish defence.
The visitors held out until the 59th minute before Hougaard broke blind and combined cleverly with Perry Humphreys to provide Lance with an easy run-in.
Worcester continued to make hard work of enforcing their superior numbers and with 11 minutes remaining, they too went down to 14 when Chris Pennell was sin-binned for a high tackle on Tom Stephenson, but it mattered little as the game meandered to its conclusion.
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