Lamine Yamal produced another double and Barcelona also got a goal from another 19-year-old product of its famed youth academy in a 4-2 win at Levante on Sunday.
Elsewhere in Europe, the Bundesliga’s biggest club needed a second-half winner from Harry Kane to beat the league's smallest side as Bayern Munich won 2-1 at promoted Elversberg.
Later, European champion Paris Saint-Germain looks for its first league win of the season when it goes to Brest.
Xavi Espart scored the opener for Barcelona with a low, bouncing shot from the edge of the area after getting set up by Raphinha five minutes in for his first goal with the senior squad.
Espart joined Barcelona’s La Masia academy as an under-10 player and made his senior team debut last season.
For Barca’s second, Raphinha dribbled around the goalkeeper and crossed for Yamal, who used one touch to smash it in from inside the 6-yard box.
Yamal then added a penalty shortly after the break for his sixth league goal of the season and his third straight brace in the Spanish league.
A poor back pass from Espart, who was playing as a left back, allowed Ivan Romero to pull one back for Levante. Then Roger Brugué scored again for Levante before Karim Adeyemi restored a two-goal advantage in stoppage time as Barcelona improved its perfect start with its sixth win in six matches across all competitions.
Lennart Karl put Bayern ahead early on before substitute Maurice Krattenmacher equalized for Elversberg in the 61st.
Kane's winner came in the 72nd as the England forward scored through traffic after Elversberg gave away possession under high pressing.
It was Kane's 99th Bundesliga goal in 97 matches.
Elversberg entered the match ahead of Bayern in the table after stunning two former champions: Bayer Leverkusen and Borussia Moenchengladbach.
Erling Haaland’s hotly contested goal settled the Manchester derby.
The Norwegian struck in the 60th minute at Old Trafford to seal a 1-0 win for 10-man Manchester City over fierce rival Manchester United in the Premier League.
At first, the goal was ruled out for offside, but after VAR review the onfield decision was overturned. That sparked a roar of celebration from the away fans.
Coventry’s nightmare start to the season continued with a 5-0 home loss to Brighton.
Dan Neil scored a double and Rangers beat Celtic 3-0 in the first Old Firm derby of the season — in the Scottish league cup quarterfinals.
Celtic fans were barred from the game following a Scottish league review of the disorder that marred the Scottish Cup quarterfinal match between the teams in March.
There were no immediate reports of disorder from the latest encounter.
Napoli ended a run of three straight losses across all competitions by beating visiting Bologna 1-0.
Midfielder Stanislav Lobotka scored in the 66th.
Juventus was visiting Sassuolo later.
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