Julen Lopetegui replaces Joaquin Caparros who had been in charge of the side on an interim basis since March.
Reyes last played for Spanish second tier side Extremadura.
Sevilla have 55 points from 36 games, and are currently in fifth place on the board.
Caparros is not the first Sevilla coach to be diagnosed with cancer.
The win takes Sevilla up to 6th on 46 points, level with Valencia and 1 point behind Getafe who occupy the final Champions League spot with 8 games left.
Gerald Deulofeu is riding the wave of a dream season for the Premier League club, who have European football and FA Cup glory in their sights.
Messi was supposed to be lacking fitness and Barca struggling for form but both delivered a resounding response.
Lazio suffered their 3rd straight defeat in all competitions.
Real Madrid has its hopes lifted as Barcelona fumbles.
Some 40 people are involved in the clashes near the Colosseum which is broken up by police in riot gear.
Felipe Caicedo forces a penalty just before the break and converts from the spot for his second goal in.
2 goals in a 2-minute spell after the break helped Barcelona race ahead.
Barcelona will have an uphill task to reach the last 4 when the 2nd leg takes place next Wednesday.
Casemiro's bending effort in the 78th minute and Modric's injury-time finish settled a compelling contest of third against fourth but Madrid were dominant in the second half.
The draw leaves Atletico 2nd in the standings on 35 points with Sevilla 3rd on 33.
The visitors were the ones celebrating at the final whistle but they head into the winter break two points behind Atletico Madrid and five adrift of leaders Barcelona.
It was the home side who eventually broke the deadlock early in the second half.
Sevilla slid down to second place in the standings on 27 points after 14 games, one behind leaders Barca.
Sevilla prevailed after the visitors' Turkish forward Enes Unal had two goals ruled out for offside in the second half.
Sevilla's 0-0 draw against Real Sociedad gave Barcelona an advantage in the race to win La Liga.
Messi scored and then went off injured as Barca beat Sevilla 4-2 at Camp Nou.
Sevilla will play against Barcelona with first place in La Liga on the line.
Barcelona's 1-1 draw against Valencia caused them to surrender their La Liga lead to Sevilla.
Arsenal and AC Milan beat Qarabağ and Olympiakos respectively, while Sevilla lost to Krasnodar.
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