Inter Milan needed to win to hold off hard-charging Atalanta in the race for third and took the lead in the fifth minute when Young was left unmarked to volley in Sánchez’s cross.
Sánchez got on the scoresheet himself 15 minutes later, striking a penalty into the bottom left corner after Victor Moses was tripped by Aleš Matějů.
It was confirmed earlier on Wednesday that the Manchester United forward will remain on loan at Inter until the end of the Serie A season.
Inter had struggled since the season resumed after it was halted because of the coronavirus pandemic but it all but wrapped the match up on the stroke of halftime when D’Ambrosio headed in Young’s cross.
And Sánchez set up another seven minutes after the break with a free kick which was headed in by Gagliardini.
Inter coach Antonio Conte brought on Candreva, Eriksen and Romelu Lukaku midway through the second half and the latter two combined for Inter’s fifth in the 83rd minute, with Eriksen tapping in after Lukaku’s effort was parried.
Candreva, who had earlier hit the crossbar, finished off the scoring five minutes later.
AC Milan was gifted an equalizer as 10-man Spal threw away a two-goal lead to draw 2-2 and give up precious points in its bid to escape relegation.
Spal defender Francesco Vicari diverted a cross into his own net in stoppage time.
Spal had played the entire second half with 10 men after Marco D’Alessandro was shown a straight red card for a challenge on Theo Hernández.
Milan struggled to create anything before Zlatan Ibrahimović made his comeback from injury as a 65th-minute substitute. The Rossoneri immediately appeared more dangerous and Rafael Leão got his side back into the match 11 minutes from time.
Spal had scored both its goals in the first half hour. The first was a scrappy goal from Mattia Valoti but the second was a magnificent lob from 30 yards by Sergio Floccari.
Spal moved off the bottom of the table but is still seven points from safety.