Chelsea striker Torres headed the world champions in front early on and, after Kim Do-Heon had equalised for the Koreans just before the break, second-half strikes from Xabi Alonso, Santi Cazorla and Alvaro Negredo ensured a highly satisfactory evening.
The match in Bern, Switzerland, was Spain's penultimate outing before they defend their European Championship title. They play China in Seville on Sunday before heading to the tournament.
Del Bosque told the Spanish football federation's website: "We leave happy because we have had a few fantastic days' training, no injuries, we've played two games and there has been a magnificent relationship among the group."
Torres' goal means he is now the fourth highest Spanish goalscorer of all-time and Del Bosque was particularly pleased with his contribution.
"He is one of those players that offers speed, movement and combination play with his team-mates," Del Bosque said. "He seemed delighted with the goal and this is good for everyone."
Del Bosque was still without the nine Barcelona and Athletic Bilbao players who will join the squad in preparation for the European Championship on Friday, having been allowed time to rest after the Copa del Rey final, so six players who had missed out on the 23-man squad were included.
"Everyone has been great," Del Bosque said, "even though they know come Friday they will not be here.
"This hasn't just been a preparation but they have put in place the roots for the future of the national team.
"The Barcelona and Athletic players return to activity when we get back for the friendly against China. I hope we have a great atmosphere there and it will be a good send-off before the Euros."