Man Utd blew neighbours Manchester City out of the water to meet the Chilean's wage demands and sacrificed Henrikh Mkhitaryan, a slightly younger player with longer left on his contract, to get him through the door at Old Trafford. Then there was that piano video.
But what fans were greeted with when the hysteria died down and the actual football started was...well, not a lot in all honesty.
Sanchez made his United debut in the most unglamorous of settings, an FA Cup fourth round tie away from home against Yeovil Town. He largely impressed in the 4-0 victory, although it was only Yeovil and his performance was also noted for how many times he gave the ball away.
Then came his first United goal a few days later in a Premier League fixture against Huddersfield, converting the rebound from his own missed penalty.
Sanchez later went on to bag two assists in the dramatic 3-2 comeback in the Manchester derby that delayed City's Premier League title party and he also scored a crucial equaliser in the FA Cup semi final against Tottenham at Wembley.
However, aside from those isolated moments, his overall impact was disappointing to say the least - Sevilla? Chelsea? Based on those four months, his arrival certainly wasn't worth the hype or the worrying side effect of pushing Marcus Rashford and Anthony Martial to the fringes.
Now, the situation is different. Arriving at a new club partway through a season can be difficult for any player as they try to adjust to new everything and hit the ground running. Last season proved to be no exception for Sanchez and the fact that he has already enjoyed a bedding in period and has now also completed a full pre-season in Man Utd colours will help no end.
What is arguably more important is that he has also had his first proper summer break in five years. Not since he has been playing in England had Sanchez previously been able to go on holiday straight after the end of the season in mid May and not return to formal training until pre-season in early July.
The summer that he joined Arsenal he was at the World Cup, followed by successive Copa America tournaments in 2015 and 2016 - both of which Chile won. He was then also bound by international commitments last year at the Confederations Cup, with Chile again reaching a final.
The fact that his country failed to qualify for the 2018 World Cup, while heartbreaking at the time, actually came as a blessing in disguise for Sanchez, who would have been looking at fifth consecutive summer with a delayed holiday and a rushed or non-existent pre-season.
Being left out of Chile's squad for the end of season friendlies against Romania, Serbia and Poland even meant the break could start sooner. It allowed him to return home to northern Chile, where he did some light altitude training in the desert, before linking up fresh with United.
It seems like little coincidence that Sanchez, back to his sharp and explosive former self, has been United's best player in the handful of friendlies they have played, finding the net against both AC Milan and Real Madrid.
Given that Paul Pogba and Romelu Lukaku will both only be working their way back to fitness as the season begins, and Antonio Valencia and Nemanja Matic are nursing injuries, Sanchez's role only becomes more important as United look to get off to a strong start.