The Iceland midfielder fired home from 40 yards within seconds of the restart in Croatia as Everton held on for a 1-1 draw.
The Iceland midfielder fired home from 40 yards within seconds of the restart in Croatia as Everton held on for a 1-1 draw in the return leg of their play-off tie after Jordan Pickford saved a second-half penalty from Ahmed Said.
Josip Radosevic drilled the home side into a 1-0 lead on the night in the closing minutes of the first half, but Everton's £45 million ($58 million, 49.4 million euros) newcomer combined with Pickford to help the Toffees clinch qualification.
Patrick Cutrone scored the only goal as AC Milan won 1-0 away to Macedonian outfit Shkendija to complete a thumping 7-0 aggregate victory, but last season's runners-up Ajax crashed out against Rosenborg.
The Dutch giants trailed after last week's 1-0 reverse in Amsterdam but looked to have turned the tie around in Norway before two late goals from Nigerian substitute Samuel Adegbenro sent Rosenborg through 4-2 on aggregate.
Marseille cruised to a 3-0 home win over Domzale of Slovenia courtesy of a Valere Germain brace and a goal from Florian Thauvin to advance 4-1 over the two legs.
Zenit St Petersburg overturned a 1-0 first-leg deficit as Russia international Aleksandr Kokorin netted a brace, including the winner on 105 minutes, to sink Utrecht 2-1 on aggregate following extra time.
However, Fenerbahce joined fellow Turkish giants Galatasaray on the European sidelines after slumping to an embarrassing 4-1 aggregate defeat to Macedonians Vardar after a shock 2-1 home loss.
Galatasaray were stunned by unfancied Swedish side Ostersund last month in the second qualifying round.
The draw for the group phase will be conducted at 1100 GMT in Monaco on Friday, with 48 teams -- including Arsenal and 2016-17 semi-finalists Lyon -- to be placed in 12 pools of four.