The Tottenham Hotspur midfielder lashed home a late leveller after a spell of pressure for Aidy Boothroyd’s side, who had fallen behind to a first half penalty.
The Young Lions lined up in an attacking formation, with Coventry City’s League One player of the month Adam Armstrong at the front of the attack.
Croatia 1-1 England
Monday 7 September 2015
Sveti Josip Radnik Stadion, Zagreb
He had Tammy Abraham and Karlan Ahearne-Grant either side behind him with Patrick Roberts in the No10 role.
Despite the firepower on display, the Young Lions struggled to break down the resolute defence of their hosts in the opening period. They enjoyed plenty of neat build-up play, but the killer pass was lacking.
They then found themselves a goal down after Callum Connolly was penalised for a foul inside the area after a coming together, with Ivan Bozic slotting home to give Croatia the lead.
England regrouped at the break and came out fighting, although they had goalkeeper Sam Howes to thank after he produced a splendid save to deny Matija Fintic grabbing a second for the hosts.
Boothroyd’s Young Lions began ramping up the pressure as they won two corners in quick succession. A fine delivery by Abraham was scrambled wide with several attackers lurking and Dael Fry headed inches over the bar after Roberts had won England a corner.
Moments later his fellow centre-half Taylor Moore, on at the break for Clarke-Salter, came close again from a corner as his header was saved by the keeper.
The momentum was building as sub Sheyi Ojo sent an effort wide after meeting Ahearne-Grant’s cross.
Something had to give and the home defence were finally breached with 18 minutes remaining as Onomah lashed home an equaliser.
The visitors could smell blood, and Armstrong was denied by the goalkeeper after timing his run to perfection and Abraham’s close-range effort was denied by a brave block from the defender.
Onomah then nearly had his and England’s second. Ahearne-Grant’s good run and shot was saved by the keeper, but the goalscorer sent the rebound effort wide of the target.
Dominic Solanke, who netted in the 3-2 win over Germany on Friday, was introduced from the bench for the final ten minutes in search of a winner.
However, it was West Ham keeper Howes who would be the hero as he made another fine stop to deny a long-ranger and Croatia a late and undeserved winner.
Next up for England will be October’s European Championship first round qualifiers in FYR Macedonia. They will face the hosts, Italy and Finland in group four.
England (4-2-3-1): 1 Sam Howes (West Ham United); 2 Kyle Walker-Peters (Tottenham), 5 Dael Fry (Middlesbrough), 6 Jake Clarke-Salter (Chelsea, Captain), 3 Callum Connolly (Everton); 4 Louis Reed (Sheffield United), 8 Josh Onomah (Tottenham); 11 Karlan Ahearne-Grant (Charlton), 10 Patrick Roberts (Manchester City), 7 Tammy Abraham (Chelsea), 9 Adam Armstrong (Coventry, on-loan from Newcastle)
Subs: 15 Taylor Moore (RC Lens) for Clarke-Salter 46, 19 Sheyi Ojo (Wolves, on-loan from Liverpool) for Roberts 65, 20 Dominic Solanke (Vitesse Arnhem, on-loan from Chelsea) for Ahearne-Grant 77, 16 Jordan Rossiter (Liverpool) for Onomah 84, 17 Lewis Cook (Leeds) for Reed 84.
Subs not used: 13 Freddie Woodman (Crawley, on-loan from Newcastle), 12 Jonjoe Kenny (Wigan, on-loan from Everton), 14 Tafari Moore (Arsenal), 18 Ainsley Maitland-Niles (Ipswich, on-loan from Arsenal)
Bookings: Connolly 26
Goals: Onomah 72