This was a derby debut to enjoy for Jose Mourinho. Tottenham may not have had much to savour this season but, with three games to go, they are now North London’s top team. Toby Alderweireld leapt highest to condemn Arsenal to just a third league defeat of 2020 and Spurs leapfrogged them in table. A fixture that often ranks among the most entertaining of the campaign lived up to its billing, with each side rattling the woodwork with thunderous strikes, but ultimately Arsenal’s defensive difficulties cost them. They have conceded many a set-piece goal over the years and the latest felt painful as Alderweireld rose above Kieran Tierney to head in Son Heung-min's corner. It was not the only thing Arsenal could regret. Having taken the lead in wonderful fashion through Alexandre Lacazette, they lost it 137 seconds later, and in avoidable fashion. The influential Son levelled and, after just two wins in 11 games and a dreadful display in drawing with Bournemouth, Spurs had something to celebrate. There was immediate improvement in one respect. Tottenham mustered more shots on target in the opening seconds than they did in Thursday’s sorry stalemate. While Emi Martinez held Lucas Moura’s long-range effort, it was at least a welcome statement of intent and the Brazilian continued to exude positivity. He provided the defence-splitting pass when Harry Kane perhaps should have scored a record 11th derby goal. The striker wandered in behind David Luiz but could not quite clear Martinez with his lob. It was, though, part of a ploy to get Kane running in behind the Arsenal defence and, with 10 minutes to go, the same combination of Moura and Kane brought another save from Martinez. The resulting corner brought Alderweireld’s decider. Mourinho played a 4-4-2 formation, with the recalled Son joining Kane in attack and reaped a reward for granting the South Korean a more central role. Tottenham’s equaliser nevertheless owed much to Arsenal. Their recent fine defensive record was all the more impressive because of the flaws the personnel possess and an individual error cost them. Sead Kolasinac failed to pick out David Luiz with a poor pass. Instead, Son anticipated it and dinked his shot over Martinez. A later mistake by Shkodran Mustafi almost allowed Spurs to score a second, though blunders were not confined to one side. The erratic Serge Aurier was doubly culpable for Lacazette’s opener. The Frenchman had gone more than a year without an away league goal before scoring at Wolves last week. Eight days later, he had another. Perhaps he would not have started but for Eddie Nketiah’s red card against Leicester, but the striker made the most of his opportunity. He unleashed a thunderbolt that flew past his compatriot Hugo Lloris and into the top corner. Indeed, it was a rare occasion when the three most expensive players in Arsenal’s history started together, with Nicolas Pepe, Pierre-Emerick Aubameyang and Lacazette forming the forward line. The captain oozed menace and, four minutes before Lacazette broke the deadlock, there was some surprise that he missed his kick when Hector Bellerin picked the captain out with a low cross. His persistence did not quite yield a goal to help him in his pursuit of second successive Golden Boot. After Pepe whistled a shot just wide, Aubameyang came similarly close with a free kick. He was nearer still when he rifled a shot against the bar after being found by his friend Lacazette. With 12 minutes remaining, Lloris made a diving save from Aubameyang’s volley. The other man to strike wood was a less likely candidate. Ben Davies is scarcely renowned for his long-range shooting but he was inches from scoring with a ferocious hit. Martinez did wonderfully well to tip it on to the bar. Once again, Bernd Leno’s deputy impressed in the absence of the injured German. A second-half dive at Son’s feet was also impressive. Yet Spurs were muted for much of the second half. Arsenal had two more days to prepare, Mourinho was reluctant to bring on substitutes but, instead, his starting 11 found a second wind and a second goal. For Mikel Arteta, a first North London derby ended in disappointment. It was a victory for management’s old guard against the young pretender.