Barcelona beat fourth-tier Barbastro 4-0 in the Copa del Rey round of 32 on Saturday, with striker Robert Lewandowski scoring either side of the break for the visitors.
Defender Eric Garcia put Barca in front with a bullet header in the 21st minute before Lewandowski nodded home from close range 10 minutes later.
The Poland striker added a third goal two minutes into the second half with a simple low finish from near the penalty spot and Pablo Torre made it 4-0 after capitalising on an error by Barbastro goalkeeper Arnau Fabrega.
"We had to start the year like this," coach Hansi Flick told a press conference. "We were very good in defence. We didn't give our rivals any chance."
The win saw Flick reach the 100th victory of his managerial career while Barcelona emergency signing Wojciech Szczesny made his debut in goal for the club.
Former Poland keeper Szczesny came out of retirement when he joined the LaLiga giants in October to replace the injured Marc-Andre Ter Stegen but had to wait to make his debut while his rival between the posts Inaki Pena maintained good form.
Barcelona took the lead when defender Ronald Araujo nodded on a long pass inside the box by Frenkie De Jong for Garcia to net into a bottom corner.
Araujo was making his season debut after suffering a hamstring injury in July during the Copa America.
"Ronald was injured but today we saw that he is fine," Flick said. "We have to be careful with him but he played well for 90 minutes. He is a leader, a captain. It's good to have him."
The hosts thwarted many of the visitors' attempts but Lewandowski, LaLiga's top scorer with 16 goals, doubled the lead after the ball deflected off a defender.
The 36-year-old added another goal after the break as Barcelona continued to dominate possession, with around 80% throughout the game.
Torre sealed the win in the 56th minute, calmly scoring after home keeper Fabrega failed to find one of his defenders with a low pass which ended up at the feet of the Barca midfielder instead.
Barcelona, who face Athletic Bilbao in a Spanish Super Cup semi-final on Wednesday, rested forward Raphinha, while midfielder Marc Casado and defender Alejandro Balde remained on the bench.
Aragonian club Barbastro sit 16th in Group Two of the Segunda Federacion.
The two teams met at the same stage of the Copa del Rey last year when Barcelona won 3-2.