Teenager Ansu Fati offered Barcelona a glimpse of what life may be like without Lionel Messi with a starring role in Sunday's 4-0 win against Villarreal.

Fati, 17, helped Barca put a tumultuous summer behind them with two goals as Ronald Koeman's side made the perfect start to the new La Liga season at Camp Nou.

Messi was also on target, scoring from the penalty spot after Fati had been fouled, in what was his first competitive appearance for the club since he tried to leave last month.

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- Ratings: Fati 9/10, Messi 7/10 in win over Villarreal

Fatk and Messi almost linked for another goal in the second half, too, and the youngster said he is happy the club captain ended up staying.

"Playing with Messi has been a dream since I was a kid and now I am doing it," Fati, who joined Barca's academy in 2012, told reporters.

"He always helps me and gives me advice, not just on the pitch but also in training. I am playing alongside the best players in the world and I try to make the most of every opportunity and every game."

Ansu, who doesn't turn 18 until Oct. 31, has now scored 10 goals for Barca since making his senior debut last August.

Koeman was delighted with his match-winning performance but warned him he still needs to improve as he looks to establish himself in the side following last year's breakout season.

"Ansu's a young player who has to find consistency in his game," the Dutch coach said in a news conference. "He's a good kid. He's open to listening and improving and he showed today that he has a huge future ahead of him at Barca.

"We know he's only 17 and there are things he can improve. Sometimes he lacks concentration. One of my criticisms of him after the friendly against Elche was his performance wasn't optimal.

"I couldn't say that today. Today, I told him it was [optimal]; that he played great. This is what he always must look for in his performances: not just creating and scoring goals, but the width he offered was important. We were able to take advantage of his qualities."

Ansu started in a four-man attack against Villarreal alongside Messi, Antoine Griezmann and Philippe Coutinho, who has returned from a season-long loan with Bayern Munich.

The deal that sent Luis Suarez to Atletico Madrid has left Barcelona without an out-and-out striker and Koeman confirmed he would like to add another attacker to his squad.

Sources have told ESPN Barca are keen on Inter Milan's Lautaro Martinez and Lyon's Memphis Depay, but with the club unable to spend big in the market, and Koeman said he will work with what he has if no one new arrives.

"It's always good to have a No.9, to have another plan upfront," he said. "But we can play perfectly without an outright No.9 on the pitch."

All Barca's goals against Villarreal came in the first half, with Pau Torres' own goal following Fati's brace and Messi's penalty. Koeman said it was "normal" that the rhythm dropped after the break given this was his side's first game of the season.

Barca are back in action on Thursday when they travel to Celta Vigo, with Sevilla next up at Camp Nou next Sunday.