In the first match for FC Barcelona since Xavi Hernández decided he'd stay, it was quite a mixed bag. The defense was honestly atrocious, but the front line played well and managed to bag 4 goals. At the end of the day, it would be three points to try to renew the good vibes. Let's take a look at each player's performance.
Goalkeeper
Ter Stegen - 5/10: He's never been one to exactly play it safe. He likes to showcase his dribbling at times, as well as his passing. However, if you play with fire often enough, you're going to get burned. He tried a chip over Hugo Duro that had no upside and a lot to lose, and conceded an extremely silly goal. Barça went on to win, sure, but mistakes like that simply can't happen in any match and those errors shouldn't be allowed. If they are, they happen in bigger games as well.
Defenders
Cancelo - 6/10: He seems to be allergic to defense. There was a stretch of games that masked this, but the recent ones have shown it extremely clearly. Due to his inability to track back, Cubarsí and Koundé often had to deal with Valencia's speed down the left, which made for some shaky moments.
Cubarsí - 6/10: It was a rare bad game from Cubarsí. One has to wonder if he's tired after playing so many matches, but it may simply have been a bad matchup for him. He was chasing after Peter for long stretches, and the Valencia player's speed was too much at times. He misjudged a long ball and allowed him an opportunity (good thing the shot was poor). He also had the chance to drive the ball forward and draw defenders more than once, but he didn't take those opportunities.
Araújo - 5/10: Araújo has tremendous physical capabilities, but he depends on them far too much. The recent string of matches has proven that. He can play on the line between physical play and fouling, but if that doesn't work, it's just a foul. He gave up a clear penalty on a challenge he didn't even need to make. He needs to play smarter and anticipate situations to snuff them out before they arrive, not react afterwards and risk fouling on needless tackles.
Koundé - 7/10: There was a stark difference between Barça's offensive game in this one and their defensive play, but Koundé personally bridged that gap well. He defended well, but he also had some success pushing up and combining with Fermín and Yamal. He briefly switched positions with Araújo and didn't skip a beat. He seemed like the only sure-footed defender in this one.
Martínez - 7/10: Despite almost giving up a penalty as well, he defended quite well throughout the second half. He is and has been a solid defender throughout the season, mainly because of his anticipation, something he could honestly teach Araújo about.
Midfielders
Christensen - 8/10: Christensen flirted with playing a 10 role for long stretches in this match. He looked quite good in there, too, taking advantage of Barça's numerical superiority to go higher and combine with Fermín, Yamal, and Gündoğan. Personally, it would've been nice to see Gündoğan there instead, but it was interesting to see the Dane play in an advanced position. However, him being so high up meant he left the back-line exposed to counter attacks.
Gündoğan - 8/10: The German was calm personified in a game that was at times chaotic and rushed. He held up the ball well and allowed Barça to keep their overwhelming possession stats up. Especially in the second half, he was a big part of Barça's many chances and ultimately their win.
Fermín - 9/10: Even ignoring his beautiful headed goal, Fermín was Barça's best player in this one. His never-ending movement freed up so much space for Yamal, and his typical runs in behind created crossing opportunities throughout the first half. He's a different kind of player for this team, one that can create goals from the midfield himself, and as such is invaluable. The goal was also important, giving Barça the lead early on.
Roberto - 7/10: He was good in this one, helping Barcelona keep a steady pressure in the second half. He, along with Gündoğan, did a lot to break down Valencia when they went down to 10 men. That constant pressure would eventually pay off with 3 more goals.
Forwards
Yamal - 7/10: He and Fermín were making defenders look silly down the right side for the whole first half. While the plays didn't quite pay off, he was a part of several dangerous actions and crosses, even forcing Valencia's two goalkeepers to intervene often and forcing several corners. He's extremely smooth out there, and he showed it again.
Lewandowksi - 9/10: The Polish striker finally had a massive game. He tied the match up just after halftime, and he would follow it up with two more goals to seal the win. He has improved quite a bit since he stopped dropping back so much and just focused on his role. Barça will need a similar Robert in their next match against Girona.
Raphinha - 7/10: Raphinha gave Cancelo a ton of space out wide with his movement inside and out. Raphinha has strangely been better since moving from his natural right side to the left, and this may be because he's playing less like Yamal, a traditional winger, and more like an interior, using the half-spaces to find angles. He also pops out when he needs to, however. Against a young team like Valencia, he seemed to find plenty of space.
Ferran - 7/10: There weren't too many opportunities for him to score directly, but he did well to cause some hesitation on the Valencia defenders' part. This helped Lewandowski spring free for the final two goals. Ferran hasn't played much recently, which is a bit puzzling to me. He's a more versatile player than someone like Lewandowski, and he may need more minutes.
Félix - 6/10: Brought on to help regain the lead, but he didn't quite provide many opportunities for Barça. He mainly served to take up space for Ferran and Lewandowski, and in this sense he played his role well.
A victory for an FC Barcelona team that now needs to travel to Montilivi to face Girona in a pivotal match. Not only is a second place on the line, but so is the pride and title of the best team in Catalunya.