Alberto Contador (Tinkoff-Saxo) cut the Polish rider's lead to just 16 by winning the stage but Kwiatkowski is confident he can defend his lead until the end of the weeklong race on Tuesday.
"I'm really happy that I'm still in the leader's jersey," Kwiatkowski said.
"We expected some big attacks from Contador and Quintana, and they did them. They really pushed me to the limit but I'm really thankful to Wouter Poels, who lead for seven kilometres on the climb, and Rigo Urán because they really did a good job for me. They set a good tempo on the last climb and I didn't lose so much time."
"I knew that I couldn't follow the attacks because they could really blow me up but I was able to handle the small difference between us. That's my style, my technique."
Kwiatkowski praised Alberto Contador and said he expects him to attack on the steep wall finish to Guardiagrele. Yet he is ready to take on Contador in the final, decisive time trial stage on Tuesday.
"He was strong. He has this day and tomorrow where he can gain seconds on the GC. He's the biggest contender for winning the whole of Tirreno. It's normal that he won. Congratulations to him," Kwiatkowski said.
"Everything's going well for me but tomorrow is the last mountain stage. I expect even more attacks tomorrow than today because the climbers know they can gain some time. I'll try to do my best and my team as well."
Time trial showdown
Kwiatkowski is ready for a show down with Contador on the Muro di Guardiagrele on Sunday and then in the final flat time trial in San Benedetto del Tronto on Tuesday.
Contador's time trial ability is well known and has helped him win Grand Tours. However Kwiatkowski knows that he beat the Spaniard by 20 seconds at the Volta ao Algarve time trial just three weeks ago.
"I'm pretty confident about my time trial skills," he said.
"But you never know how it will go. It's on the last day after a hard Tirreno-Adriatico. Maybe ability will not be so important, it will be about who has more energy. I feel pretty confident but you can have a good day or bad day. We'll see."