Defenders in the Bundesliga have had a year and a half now to think up ways of constraining Erling Braut Haaland. Evidently, they need to think harder. The giant Norwegian, who turned 21 last month, has just begun his second full season with Borussia Dortmund in the same irrepressible way he started off his career in Germany. Haaland recorded a hat-trick of assists against Eintracht Frankfurt on the league’s opening weekend. Being Haaland, he scored two goals as well, one with his left foot, one with his right, both made possible by that rare, uncontainable blend of speed, body strength and quick wits that make him one of the two most coveted forwards of his age group. The other is Kylian Mbappe, 22. Mbappe and Haaland keep an eye on each other’s performances. On Saturday, both were excellent. A few hours after Haaland set up goals for Marco Reus, Gio Reyna, and Thorgan Hazard in the 5-2 win over Frankfurt, Mbappe was propelling Paris Saint-Germain towards a 3-0 half-time lead at home to Strasbourg at the Parc des Princes. By full-time, Mbappe had his hat-trick of assists, crosses for Julian Draxler and Pablo Sarabia plus a rifled shot deflected for an own goal off Strasbourg’s Ludovic Ajorque in PSG’s 4-2 win. There were sizeable crowds at Dortmund and in Paris, which ought to have been a significant boost. Most of Haaland’s 62 goals - in 61 matches - for Dortmund have been scored in empty stadiums, because of the Covid-19 restrictions imposed only two months after he joined the club in early 2020. Mbappe became Ligue 1’s leading scorer last season in front of very few paying spectators. At the weekend, he played in front of a full 46,000 at the Parc des Princes for the first time since before the public health crisis. Not all of them, though, had come ready to applaud Mbappe. His name was booed when it was read out ahead of kick-off, and when it was listed in the starting XI an hour earlier. It was cheered at the same time, but if the jeerers were a minority they were a loud minority. The hostility towards Mbappe struck an odd note on an evening where fans had arrived early specifically to clap and chant for superstars. Mainly for Lionel Messi, who was presented to supporters as PSG’s sensational summer capture, alongside the other distinguished new arrivals, Achraf Hakimi, Gini Wijnaldum, Gigio Donnarumma and Sergio Ramos. Their new club put on a glitzy pre-match show to welcome them, though Messi, Ramos and Donnarumma were not yet deemed ready to make their debuts. Nor were Neymar, Angel Di Maria, Marquinhos or Marco Verratti fully recuperated from their extended international tournament action for their countries during the summer. That left Mbappe as the leading star on the pitch. PSG needed his brilliance, after slipping from 3-0 ahead to 3-2. One of Mbappe’s many jet-propelled runs set up Sarabia’s goal to ease concerns. “I am very happy with Kylian,” said head coach Mauricio Pochettino, and, referencing the earlier booing, added, “Kylian knows how to stay focussed.” Why the hostility from sections of the PSG support? Mbappe is stalling on renewing a contract that expires next June. He knows Real Madrid are eager to sign him, and he has made no secret of his ambition to play some of his career outside France. As things stand, he could officially open talks with Madrid, or any other club, in January, and leave PSG for free in less than 10 months time. PSG hope that a dazzling season alongside Messi, Neymar and company will persuade Mbappe his long-term ambitions are best served in Paris. Until he commits to that, he can expect coldness from some fans. Haaland also plans to explore transfer options next summer, but his situation is different. Unlike Mbappe, who has this summer been joined at PSG by a parade of world-beaters, Haaland has seen a favourite ally, the master of assists Jadon Sancho, depart his club for Manchester United. Unlike Mbappe, Haaland has a contract with his current club until 2024. A sale next June would, assuming he suffers no sudden loss of form or fitness, bring to Dortmund greater funds even than Sancho’s €85m move. In the meantime, Haaland has no doubt about how he is valued in Dortmund hearts. “His consistency is amazing,” beamed the club’s head coach Marco Rose, looking ahead to Tuesday's German Super Cup meeting with champions Bayern Munich. The venue is Dortmund’s Westfalen stadium, where Haaland’s name was still being chanted long after the final whistle on Saturday.