Lukaku scored his first goal for six games in Abu DhabiChelsea will meet Brazilian side Palmeiras in the Club World Cup final after edging past Al-Hilal at the Mohamed bin Zayed Stadium in Abu Dhabi.
Romelu Lukaku scored the only goal in the first half.
The Blues will now look to lift the only trophy that has evaded them across Roman Abramovich's 19-year ownership of the club.
Boss Thomas Tuchel missed the game as he was isolating after testing positive for Covid-19.
Chelsea dominated from the start against the Saudi Arabian side, and their breakthrough came from Lukaku just after the half-hour mark.
Kai Havertz's left-wing cross was inadvertently headed into the Belgian's path by Yasser Al Shahrani, and he rifled home from point-blank range.
It was Lukaku's ninth goal of the season and ended a six-game drought, after he missed a couple of opportunities earlier in the match.
Two minutes after the break, Havertz burst through on goal and clipped the post from a tight angle, despite having Lukaku and Hakim Ziyech for support in the area.
Asian champions Al-Hilal barely threatened until Mohamed Kanno shot over from distance after combining well with former West Bromwich Albion midfielder Matheus Pereira.
Chelsea keeper Kepa Arrizabalaga then denied Moussa Marega from eight yards out, while Odion Ighalo and Kanno saw shots blocked as Chelsea struggled to put the game to bed.
But the European champions held on in the end and, in Saturday's final, will have the chance to avenge defeat in this competition a decade after their last appearance.
Line-ups
Al-Hilal
Formation 4-1-4-1
1Al Mayoof
2Al Burayk20Jang Hyun-Soo5Al Bulayhi12Al Shahrani
6Cuéllar
17Marega28Kanno15Costa Pereira29Al Dawsari
9Ighalo
1Al Mayoof2Al Burayk20Jang Hyun-Soo5Al BulayhiBooked at 84mins12Al Shahrani6CuéllarBooked at 66mins17Marega28Kanno15Costa PereiraSubstituted forDelgado de Oliveiraat 82'minutes29Al DawsariSubstituted forCarrilloat 82'minutes9IghaloSubstitutes
11Al Shehri13Al Obaid19Carrillo21Al Owais32Al Mufarrij33Al Jadani43Al Juwayr66Abdul Hamid70Jahfali88Al Tuhayfan Al Yami96Delgado de OliveiraChelsea
Formation 3-4-2-1
1Arrizabalaga
4Christensen6Thiago Silva2Rüdiger
28Azpilicueta5Jorginho8Kovacic3Alonso
22Ziyech29Havertz
9Lukaku
1Arrizabalaga4Christensen6Thiago Silva2Rüdiger28Azpilicueta5JorginhoSubstituted forKantéat 45'minutes8KovacicBooked at 81mins3AlonsoSubstituted forSarrat 87'minutes22ZiyechSubstituted forMountat 72'minutes29Havertz9LukakuSubstitutes
7Kanté10Pulisic11Werner13Bettinelli14Chalobah16Mendy17Saúl18Barkley19Mount20Hudson-Odoi23Kenedy31SarrReferee:César Arturo Ramos PalazuelosLive Text
Match ends, Al-Hilal 0, Chelsea 1.
Second Half ends, Al-Hilal 0, Chelsea 1.
Foul by Andreas Christensen (Chelsea).
Odion Ighalo (Al-Hilal) wins a free kick in the defensive half.
Offside, Al-Hilal. Mohammed Al Burayk tries a through ball, but Moussa Marega is caught offside.
Corner, Chelsea. Conceded by Gustavo Cuéllar.
Substitution, Chelsea. Malang Sarr replaces Marcos Alonso.
Foul by Mason Mount (Chelsea).
Yaseer Al Shahrani (Al-Hilal) wins a free kick in the defensive half.
Foul by N'Golo Kanté (Chelsea).
Gustavo Cuéllar (Al-Hilal) wins a free kick on the left wing.
Ali Al Bulayhi (Al-Hilal) is shown the yellow card.
Substitution, Al-Hilal. Michael replaces Matheus Pereira.
Substitution, Al-Hilal. André Carrillo replaces Salem Al Dawsari.
Mateo Kovacic (Chelsea) is shown the yellow card for a bad foul.
Foul by Mateo Kovacic (Chelsea).
Salem Al Dawsari (Al-Hilal) wins a free kick in the defensive half.
Corner, Chelsea. Conceded by Mohamed Kanno.
Attempt blocked. Mason Mount (Chelsea) right footed shot from the centre of the box is blocked. Assisted by Romelu Lukaku.
Foul by César Azpilicueta (Chelsea).
