In front of 49,861, Hernandez scored with his first touch to contribute to a 7-1 rout of Airtricity League XI - the best Ireland's domestic campaign can muster. Hernandez`s third goal in as many games - one of which was against his new club - offers huge promise for the 22-year-old nicknamed "Little Pea".
Michael Owen also found the net on his first appearance of pre-season but there was nothing for Wayne Rooney during a typically industrious 45-minute display. Aside from the minor inconvenience of Rooney's blank, the major piece of bad news for United on a night when they were hardly asked to do any defending was the loss of Michael Carrick, who limped off midway through the opening period of his first game since a World Cup campaign he watched exclusively from England's substitutes' bench.
Park Ji-sung also grabbed a brace along with goals from Antonio Valencia, Jonny Evans and a Nani penalty.
Everton 2-0 Everton Chile
Jermaine Beckford and Diniyar Bilyaletdinov struck as David Moyes' Everton continued their pre-season preparations with a comfortable 2-0 win over their Chilean namesakes.
The pair were on target in the second half as the Merseyside club took on the South American side named after them for the first time in an historic friendly. Chile's Everton were founded in 1909 after the original Everton made a positive impression on a pioneering tour across the Atlantic.
The match was played for the newly-created Brotherhood Cup and could be the start of closer ties between the two clubs. The main purpose of the exercise for Moyes, however, was fine-tuning ahead of the Barclays Premier League season. And the Scot will have been pleased with a lively display from new signing Beckford and a first run-out for Marouane Fellaini since injuring his ankle in a Merseyside derby in February.
Referee Mark Halsey, who is in remission from cancer, was also given a warm reception by an appreciative Goodison Park crowd.
Hamburg 2-1 Chelsea
Frank Lampard's goal could not prevent an almost full-strength Chelsea from slipping to a 2-1 pre-season friendly defeat away to Hamburg on Wednesday night.
The England midfielder put the Blues ahead in the 24th minute, tapping Michael Essien's unselfish square pass into an empty net. But Mladen Petric capitalised on a mistake by Yury Zhirkov, on at left-back for Ashley Cole, to beat Ross Turnbull with 18 minutes to go.
Worse was to come for the Barclays Premier League champions as Heung Min Son won it for Hamburg with just three minutes remaining, inflicting Chelsea's third successive loss of the summer following defeats to Ajax and Eintracht Frankfurt.
Carlo Ancelotti named a strong side for the game in Germany, with John Terry, Branislav Ivanovic, John Obi Mikel, Nicolas Anelka, Salomon Kalou and Florent Malouda all also featuring from the start, while Didier Drogba played the second half to make his first pre-season outing following hernia surgery.
Borussia Dortmund 3-1 Manchester City
Manchester City went down 3-1 to Borussia Dortmund in their latest pre-season friendly at the Westfalenstadion. Paraguay striker Lucas Barrios put Dortmund ahead with a ninth-minute penalty only for Jo, who spent time on loan at Everton and Galatasaray last season, to level two minutes later.
Joe Hart ensured City went into half-time on level terms by diving to his right to keep out a casual Barrios penalty. But the Germans restored their lead five minutes after the break through Shinji Kagawa and Robert Lewandowski then wrapped up the win in the 81st minute.
Wigan Athletic 1-3 Real Zaragoza
Wigan lost 3-1 to Real Zaragoza at the DW Stadium as they continued their preparations ahead of the new Barclays Premier League season.
The La Liga side's 34th-minute opener came when Steve Gohouri's sliding clearance rebounded off Marco Perez who raced into the penalty area only to be brought down by goalkeeper Chris Kirkland. Jorge Lopez converted from the spot but an even worse error led to the equaliser seconds before half-time when Carlos Diogo rolled a free-kick straight into the path of Ben Watson.
After moving the ball on, the midfielder eventually laid on the pass for Charles N'Zogbia to round goalkeeper Leo Franco. However, 15 minutes from time Braulio Nobrega capitalised on a quick ball forward to clip past Kirkland before Gabriel Fernandez smashed in an unstoppable 35-yard effort.
A number of Roberto Martinez's new signings featured, with club-record transfer Mauro Boselli, the former Estudiantes striker, showing some good touches but looking short of match sharpness.