Google CEO Sundar Pichai was summoned to federal court for another time in two weeks to testify in an antitrust trial threatening to tumble a pillar of an internet conglomerate that he helped construct.

In his latest court appearance in San Francisco, Pichai spent further than two hours defending the business practices of the Google Play Store, which distributes apps for the company’s Android software that powers maximum of the world’s smartphones.

At times, the soft- spoken Pichai looked nonplussed and frustrated by the confrontational questioning he faced.

Other times he came across as a professor explaining complex subjects to the trial’s 10- person jury located just a few feet from a dais Pichai was allowed to use as he has difficulty sitting for prolonged periods.

Epic Games, the maker of the popular video game “Fortnite”, is trying to persuade the jury that a Google Play payment processing system that collects a 15 to 30 commission from in- app purchases is unethically hurting consumers and software developers. Alphabet’s GOOG,1.34 GOOGL,1.16 Google collects those commissions, according to Epic, by using its market muscle to thwart competing Android app stores — a strategy that drives up prices and discourages innovation.

Pichai’s latest testimony came 15 days after he traveled to WashingtonD.C. to take the stand in a separate antitrust trial revolving around theU.S. Justice Department’s allegations that Google has stifled competition and innovation by abusing the power of the dominant search engine that launched the company in 1998.

Although the two trials are unfolding on opposite ends of the country and are delving into different parts of a company that investors value at$1.7 trillion, they're touching upon at least two common issues — Google’s immense power and its unusual relationship with Apple, an even bigger tech powerhouse.

A crucial part of Google’s defense against allegations that its Play Store is running an illegal monopoly on Android apps hinges on the assertion that the company faces major competition from Apple’s iPhone, mobile operating system and app store.