The No.10 was in brilliant form as she netted twice, with Natasha Harding and Casey Stoney also on the mark.
Weir's opening strike on 10 minutes was something special. Picking the ball up 30 yards from goal, she turned the defender before firing an unstoppable effort beyond Anke Preuss and into the back of the net.
At the other end, the away side almost got back on level terms when a mistake let in Beverley Leon but she was denied by a great save from Siobhan Chamberlain.
Preuss then produced an outstanding double stop to keep out Alex Greenwood and Jess Clarke, but the stopper was powerless to deny the second goal on 21 minutes.
A lovely break and pass from Greenwood found Harding, whose superb first touch allowed for a clinical finish into the corner of the net.
Sunderland started the second 45 minutes strongly. Madelaine Hill struck the outside of the post with an effort from distance, before another excellent Chamberlain stop thwarted ex-Red Lucy Staniforth.
However, Weir made it 3-0 on 56 minutes by capping off a classy team move.
Great work from Harding down the right flank set up Gemma Bonner. The captain then produced a deep cross, that was sweetly pulled back across goal by Ali Johnson and Weir made no mistake from close range.
Clarke and Bonner both went close to adding further flourishes before the fourth goal arrived from a well-worked corner, when Greenwood's cross saw Stoney claim the final touch to make it 4-0.
It's now 18 goals in just five outings for Scott Rogers' charges in the Spring Series, and the team will head to Bristol on Saturday full of confidence.
Liverpool Ladies: Chamberlain, Hodson, Greenwood, Stoney, Bonner, Ingle, Charles (Johnson, 55), Coombs, Clarke, Weir (Fletcher, 75), Harding (Longhurst, 68).