Elsewhere defending champion Rafa Nadal produced a claycourt masterclass to pick apart fellow Spaniard Roberto Bautista Agut 6-1 6-1, as the world number two began his title defence in stunning fashion on Wednesday.
The victor of the last three Grand Slams made eight double faults, dropped serve four times and smashed a racquet after losing the second set to his German opponent in the second-round encounter. Is this the best that I have played on clay? No.
I've discussed several times that I find Tsitsipas rather over-rated on hard courts but on clay his stats suggest huge potential. "I thought I should have maybe stepped in and played a bit more aggressive in the second set, but credit to him for mixing up the pace and playing well".
Bautista Agut has now lost to his Spanish countryman in all three of their meetings, while Nadal improved his incredible record here to 69-4 as he takes aim at a fourth consecutive title at the event.
Third seed Alexander Zverev rediscovered traces of his best form with a 6-1, 6-4 defeat of Felix Auger-Aliassime.
The 18-year-old Auger-Aliassime, who reached last month's Miami semi-finals as a qualifier, now boasts a ranking of 33rd - up from 175th when he played here a year ago. After all, there are two more Masters in Madrid and Rome to come, concluded by his attempt to win a second French Open.
"This is the first time this season I've felt really healthy", said the 21-year-old.
"I've been training well but haven't been able to take that into matches. I started the match so tense, and then I started to play way better because I started to play with my serve, with my forehand", Cecchinato pointed out. I m starting to feel better about my game. "It s been a long hardcourt court season before the clay".
He was leading by a set and serving at 2-3 when forced to save two break points.
Fourth seed Dominic Thiem also got off to the flawless start, handling the unsafe Martin Klizan 6-1, 6-4 while sixth seed Stefanos Tsitsipas took care of Mikhail Kukushkin 6-3, 7-5.
This is not the first time Dimitrov has done it on court. This was a tough first match of the clay season.
Cilic was a set and a break down but battled back to level the match, only for Pella to seize control again in the decider and seal a 6-3 5-7 6-1 victory with plenty to spare.