Match ends, Real Madrid 3, Roma 0.
Real Madrid got their Champions League defence off to a winning start thanks to a comfortable victory over Roma.
The Spanish side, looking to win the tournament for the fourth year in a row, dominated but were frustrated until Isco curled home from 25 yards out at the end of the first half.
Gareth Bale added a second when he ran onto Luka Modric's excellent through-ball and slotted home.
And Mariano Diaz curled home late on from 20 yards for a deserved third.
Last season's semi-finalists Roma were second best throughout, although Cengiz Under forced a good diving save from Keylor Navas.
However, these two teams will both be favourites to progress from Group G, which also contains Czech side Viktoria Plzen and CSKA Moscow. The Russian visitors came from 2-0 down to draw their opening game 2-2.
Real Madrid are unbeaten in La Liga this season after the departures of boss Zinedine Zidane and their all-time top scorer Cristiano Ronaldo, who had scored or assisted exactly half their Champions League goals in his nine years at the club.
The departure of Ronaldo - the central focus of their play for years - to Juventus seems to have given some Real players a new freedom. Isco and Bale were among the players to take advantage of more responsibility, with Modric playing some sublime passes in midfield.
It took Julen Lopetegui's side 17 shots before they scored through Isco's wonderful free-kick, which he probably would not have been allowed to take next to Ronaldo last season.
Bale, who has now scored five goals in seven games this season, looked sharp and hit the woodwork before rifling his game-clinching goal across Robin Olsen into the far corner of the net.
Isco forced a good stop from close range from Olsen, who produced diving saves to deny Toni Kroos and Modric.
Second-half substitute Marco Asensio almost added a spectacular showboating third when he spun in the box to lose two defenders but his no-look shot was well saved by Olsen's leg.
Edin Dzeko's header was kept out by Navas, who was preferred to summer signing Thibaut Courtois in goal for Real.
And 25-year-old striker Mariano - in his first game since returning to the club from Lyon for £29.7m - struck late on to give Real a scoreline that reflected their dominance.
Real Madrid host Espanyol on Saturday (19:45 BST) in La Liga, with Roma visiting Bologna on Sunday (14:00 BST) in Serie A.
In the next Champions League fixtures on Tuesday, 2 October, Roma host Viktoria Plzen and Real are at CSKA Moscow (both 20:00 BST).
Match ends, Real Madrid 3, Roma 0.
Second Half ends, Real Madrid 3, Roma 0.
Goal! Real Madrid 3, Roma 0. Mariano (Real Madrid) right footed shot from outside the box to the top right corner. Assisted by Marcelo.
Offside, Real Madrid. Marcelo tries a through ball, but Isco is caught offside.
Corner, Real Madrid. Conceded by Federico Fazio.
Attempt saved. Dani Ceballos (Real Madrid) right footed shot from the right side of the box is saved in the bottom left corner. Assisted by Marco Asensio.
Attempt missed. Aleksandar Kolarov (Roma) left footed shot from outside the box misses to the right following a corner.
Corner, Roma. Conceded by Keylor Navas.
Attempt saved. Edin Dzeko (Roma) header from the centre of the box is saved in the bottom left corner. Assisted by Lorenzo Pellegrini with a cross.
Corner, Roma. Conceded by Dani Ceballos.
Corner, Roma. Conceded by Raphael Varane.
Substitution, Real Madrid. Dani Ceballos replaces Luka Modric.
Corner, Real Madrid. Conceded by Patrik Schick.
Attempt blocked. Casemiro (Real Madrid) header from the centre of the box is blocked. Assisted by Toni Kroos with a cross.
Corner, Real Madrid. Conceded by Kostas Manolas.
Attempt blocked. Marco Asensio (Real Madrid) left footed shot from the left side of the box is blocked.
Attempt saved. Marco Asensio (Real Madrid) left footed shot from the centre of the box is saved in the centre of the goal. Assisted by Isco.
Edin Dzeko (Roma) is shown the yellow card for a bad foul.
Mariano (Real Madrid) wins a free kick in the defensive half.
Foul by Edin Dzeko (Roma).
Corner, Real Madrid. Conceded by Kostas Manolas.
Attempt saved. Luka Modric (Real Madrid) right footed shot from outside the box is saved in the bottom left corner. Assisted by Daniel Carvajal.
Corner, Real Madrid. Conceded by Aleksandar Kolarov.
Attempt saved. Toni Kroos (Real Madrid) left footed shot from the left side of the box is saved in the top centre of the goal. Assisted by Mariano.
Substitution, Real Madrid. Mariano replaces Gareth Bale.
Attempt missed. Patrik Schick (Roma) left footed shot from outside the box is high and wide to the left. Assisted by Cengiz Ünder.
Substitution, Roma. Patrik Schick replaces Steven Nzonzi.
Attempt missed. Marco Asensio (Real Madrid) left footed shot from outside the box misses to the left. Assisted by Isco.
Attempt missed. Casemiro (Real Madrid) right footed shot from outside the box is close, but misses the top left corner. Assisted by Luka Modric.
Corner, Roma. Conceded by Isco.
Attempt missed. Alessandro Florenzi (Roma) right footed shot from outside the box misses to the left. Assisted by Aleksandar Kolarov following a corner.
Corner, Roma. Conceded by Casemiro.
Attempt blocked. Edin Dzeko (Roma) right footed shot from the left side of the box is blocked.
Attempt missed. Kostas Manolas (Roma) header from the centre of the box misses to the left. Assisted by Cengiz Ünder with a cross following a corner.
Corner, Roma. Conceded by Keylor Navas.
Attempt saved. Aleksandar Kolarov (Roma) left footed shot from outside the box is saved in the centre of the goal. Assisted by Steven Nzonzi.
Substitution, Roma. Diego Perotti replaces Stephan El Shaarawy.
Substitution, Real Madrid. Marco Asensio replaces Karim Benzema.
Goal! Real Madrid 2, Roma 0. Gareth Bale (Real Madrid) left footed shot from the left side of the box to the bottom right corner. Assisted by Luka Modric following a fast break.
Corner, Roma. Conceded by Raphael Varane.