The Belfast flyweight was making a dream appearance on the annual Mick Conlan St Patrick’s Day card at The Theater at Madison Square Garden but it quickly turned into a nightmare.
A bloodied Barnes was beaten by tough Texan Oscar Mojica on a split decision at the Felt Forum and his career now lies in tatters.
It was almost seven months on since Barnes sought to become the quickest Irish world champion in terms of number of fights and was defeated by Nicaraguan Cristofer Rosales at Windsor Park.
The 31-year-old had attempted to make his return to the ring in December on the Warrington-Frampton undercard in Manchester but his swing bout was forced off the bill on the night due to the card running late.
And so, Barnes was back in the ring for the first time tonight and was handed an extremely tricky task in Mojica in what looked to be a potentially precarious six-rounder – and so it proved.
The Irishman is a small to average-sized flyweight but his fight here was up at bantam against the far larger American – who was given plenty of notice and had upset previous having held 10-0 prospect Ruben Vega to a draw last time out and also beating 10-0 prospect Johnny Determan back in 2016.
Mojica’s danger was underlined in the opening seconds when a sharp shot burst Barnes’s nose. Blood gushing, the Ulsterman was put under serious pressure from the Dallas native and seemed bothered by a bodyshot but was landing flurries himself.
Disaster looked to have struck in the second as Barnes was floored by the big 26-year-old, a left hook to the body sending the Irish amateur legend down. Somehow, though, it was not ruled a knockdown and a hurt Barnes rose and fought back gallantly, rousing the crowd and landing combos to the bell.
The heavy shots continued to come from Mojica in the third but the boxing skill of Barnes would come into it more as the round progressed and he then enjoyed his best spell of success in the fourth.
Mojica, though, roared back late in the fifth with thudding blows and, going into the final round, Barnes was told by his corner that he needed a knockout. A big shot would come early from Barnes but Mojica was just too solid and was able to withstand a huge final push to see the round out.
Going to the cards a split was called with Barnes taking a 58-56 win with one judge but this was overruled, correctly, by two 58-56s for Mojica.
Barnes falls now to 5(1)-2(1) and would admit afterwards that, nose broken and experiencing difficulties with his vision, he felt he lost every round.
The double Olympic bronze medallist, double Commonwealth champion, European gold medallist, and WSB #1 then admitted that retirement is a strong possibility.
Mojica, who was excellent, improves to 12(1)-5(0)-1
Earlier on on the bill, Russian featherweight Vladimir Nikitin, Olympic rival of Conlan, struggled in a slugfest with Texan Juan Tapia, eventually claiming a six-round majority-decision win to move to 3(0)-0.
Before this, Limerick welter Lee Reeves opened the bill and improved to 3(2)-0 following a unanimous decision (40-36 x3) points win over Edward Torres.