Diaz caught Wanderers keeper Daniel Margush off his line in the 61st minute with a free-kick from 40 yards which flew into the net as Apia went on to claim a 2-1 win at Leichhardt Oval.

The defeat means APIA are the first state-league team to defeat A-League Men opponents twice in the Cup's history, having humbled Melbourne Victory at the same venue three years ago.

The result also heaps more pressure on Wanderers coach Carl Robinson, ahead of a crunch derby with Macarthur FC on Saturday.

Despite having come through a gruelling round-of-32 clash in the ACT last week against Cooma Tigers which went into extra-time, it was APIA who hit the front when American-born striker Jason Romero opened the scoring in the 27th minute.

Diaz's amazing strike made it 2-0 before a deflected effort from Tass Mourdoukoutas with 20 minutes to play sparked the Wanderers into life.

Despite dominating the final minutes against their tiring opposition, Robinson's men couldn't find an equaliser and APIA will move into the competition's quarter-finals.

Elsewhere on Tuesday, a first-half strike by Ben Waine was enough to secure Wellington a 1-0 win over Western United in an all A-League Men affair in Geelong.

Waine's goal was the Phoenix's only shot on target in a match dominated by John Aloisi's team but it was Wellington who marched into the round of 16.

Australian Associated Press